Dragon and the ISS robotic arm
image:SpaceX

The Mission

The mission goes by the name of COTS 2 (Commercial Orbital Transportation Services) and will mark the first time in history that a private company demonstrates the ability to deliver cargo to ISS. The Falcon 9 rocket will be carrying with it the Dragron spacecraft and will be launched from the Cape Canaveral Air Force Station.

It will reach orbit in just under 10 minutes from launch and is scheduled to begin a series of rendezvous tests after its third day in space. If all goes as planned, the Dragon spacecraft will dock with the space station after a few more days of tests. The robotic arm on the International Space Station will be used to assist in the operation.

Commercial Orbital Transportation Services

The Commercial Orbital Transportation Services program started in 2006 as an effort to stimulate the private sector to develop safe, reliable space craft and launch vehicles for ISS cargo delivery. To date NASA is investing in two companies to further this initiative along – SpaceX and Orbital Sciences Corp.

SpaceX successfully launched their first Falcon 9 rocket with a test Dragon capsule on June 4, 2010. This flight was followed up with a successful resupply demonstration flight on December 8, 2010. The latter proved Dragon’s ability to achieve multiple orbits and respond to ground commands.

Press Kit

For those that are interested, SpaceX has provided a press kit for the mission. The kit, a downloadable .pdf file, also contains information on ISS, the Dragon spacecraft, the COTS program and the history of SpaceX itself. You may download the file by clicking here.


©2012 Sigma Rockets and Aerospace Inc.

Figure 1 - Design Rocket

OpenRocket

In this article we will use the program OpenRocket for our design and analysis. OpenRocket is a free, open source rocket design and rocket flight simulation software which we introduced in a previous article.

OpenRocket may be found by going to the url: http://openrocket.sourceforge.net.

Drag Sources of a Model Rocket

A model rocket is composed of 3 major parts, the nose cone, the body tube and the fins. Each one of these components contributes to the aerodynamic drag of the rocket. Breaking a model rocket down to its basic components and addressing the drag on each component is a good way to start our design. The overall aerodynamic drag on the rocket may be expressed as such:

Where D_NC is the drag from the nose cone, D_BT is the drag from the body tube and D_F is the drag from the fins. We will ignore the drag created from the launch lug for the purposes of this article.

Design Rocket

For our article we will start by using the rocket you see in figure 1. The rocket stands just over 62 cm with three trapezoidal fins and a 15 cm nose cone. The body tube is 45 cm long and 5 cm in diameter and there is an 18 mm motor tube.

We will be changing various components on the design rocket and checking their drag results in OpenRocket.

Figure 2 - Comparison nose cones

The Nose Cone

The shape of the nose cone is a large contributing factor in its drag. If you recall from our first article in this series you know that a blunt object creates the most drag. A rounded streamline nose cone creates the least amount of drag.

It’s not to hard to picture more drag for a blunt flat nose cone as compared to a more streamlined one. This is similar to the discussion we had about how streamlining your hand when sticking it out of a traveling car reduces the drag you feel.

The nose cone is actually affected by both surface and pressure drag. We may determine the drag of different types of nose cones using a wind tunnel or we may use a software program such as OpenRocket to determine it.

To analyze the effect of nose cone designs in figure 2 we utilize the Drag Characteristics tab of Component Analysis function in OpenRocket. This function is found under the Analyze menu.

For our analysis we leave everything on our design rocket the same and change only the nose cone. Below is a table of the results for the analysis.

As we can see the ogive nose cone design gives us the least amount of drag for the rocket and contributes the least percentage of total drag for our design. As well it gives our rocket a lower overall drag coefficient compared to the other two designs.

The Body Tube

We will continue our design using the ogive nose cone and move on to the body tube. For body tubes there are basically two types of aerodynamic drag acting against it: surface drag and base drag. Surface drag may be reduced by having a smooth surface and finish on the body tube. Base drag can be reduced significantly by applying a boat tail, or transition to the bottom of the rocket. For our analysis we will add and compare boat tails.

The Fins

When a cross wind hits a model rocket on its flight upwards it is the fins that provide the force to correct it. It is important to have the fins large enough for this correction and small enough so that they do not provide excessive weight to the rocket. We may also change the number of fins in our design as well as the angle on which they are attached to the body tube. To keep it simple we will stick to three fins. We will also keep the fin cant angle, the angle in which the fins intersect with the body, at zero (perpendicular to the body).

In OpenRocket the user may select one of two preset fin designs or may design their own fins. We will choose the preset Trapezoidal and alter one of its parameters for our design. We will modify the sweep length of the fins. The table below shows our analysis.

Conclusion

Our article touched on just a few of the parameters that you may alter in your design to lower the aerodynamic drag for your design. Please note that we did not touch upon rocket stability which also effects the performance of your rocket. In future articles we will discuss stability.

OpenRocket is an excellent program to assist the rocket designer in the design of his/her rocket. In this article we demonstrated only a small part of what OpenRocket can do. More may be discovered by downloading the program and using it to design your our rockets.


©2012 Sigma Rockets and Aerospace Inc.

Figure 1 - Thrust curve for E9 motor

The Average Thrust

We will start with the first number that follows the letter. This number represents the average thrust of the rocket motor and is measured in Newtons. For example, an E9-6 motor, has an average thrust of 9 Newtons.

Our graph in figure 1 shows the thrust curve, or thrust vs. time, for the E9 motor. As we can see the motor reaches its peak thrust just after the 0.25 second mark and burns until the 3.1 second mark. If we were to take an average on this graph we would get 9 Newtons, the number designated in the motor code.

The Total Impulse

The letter which precedes the numbers for rocket motors and follows the first set of numbers in the case of some high power rocket motors is the Total Impulse.

Total impulse is the total power of a rocket motor. It is the product of the Average Thrust and the Burn Time and is measured in Newton-Seconds. We represent Total Impulse for our motors using ranges which are assigned to letters.

As we can see in the table below an A motor is any motor that has a Total Impulse from 1.21 to 2.5 Newton-Seconds. We can further divide our impulse chart by size specifications.

Figure 2 - Flight Path of a Model Rocket

The Delay Time

The final number in the rocket motor designation is the delay time that occurs after the thrust of the motor and before the ejection charge. An “A” may be present indicating that the delay is adjustable. Using figure 2 as a reference, the delay time is the amount of time taken from coast through apogee and right to ejection.

Figure 2 is a graphic we used in previous articles on flight analysis. The data for this graph was based on a flight with a B6-4 motor. Adding the time from the beginning of the coast phase to apogee and the apogee to ejection we get 4.6 seconds. This is close to the rating on the motor of 4 seconds.

In some cases the motor may not have an ejection charge. This would be indicated with a “P” instead of a number. Such motors are used for rocket gliders and rockets where parachute deployment is controlled with electronics.

Our Video on model rocket motor classifications

We have produced a video on model rocket motor classifications. The video is based on the information above.

©2012 Sigma Rockets and Aerospace Inc.

Figure 1 - OpenRocket flight analysis

Using OpenRocket

To find and download OpenRocket you may refer to our previous article on it.. Our test rocket was constructed with the following values:

- nose cone is Ogive, 3.4 cm in diameter and 15 cm long

- body tube is 45 cm long and 3.4 cm in diameter

- there are 3 fins designed in Freeform mode

- an 18 mm motor mount is used

- a B6-4 motor is used for both our simulation and rocket flight

- a mass component of 29 grams was added to the design so that it would weigh the same as the actual rocket

You may download the design used for this article here.

Flight Analysis

Figure 1 is a flight analysis chart from OpenRocket of our test rocket. Table 1 below compares the simulated results with the actual results recorded from our flight.

In the video of our test rocket flight the model rocket is stopped and held in place at its various points in the flight path. We’ve included the measurements taken at those points in Table 1 above.

Conclusion

As can be seen in our table above OpenRocket is able to predict parameters for a real model rocket flight. For some of the values the numbers are surprisingly close. There are many factors that may affect the actual performance of a rocket flight. For example, construction techniques play a huge role in the drag affecting the model rocket. Our test rocket was put together quite quickly. The fins were not sanded into tear drop airfoils. The finish on the fins could have been smoother. As well, if you notice in our video the rocket dips a little bit on the way up costing it some altitude.

Wind also plays a large role in the flight of a model rocket. We were fortunate to have very little wind on the day we launched the rocket. However, the dip during the burn phase most likely was caused by a small gust of wind at that moment.

In conclusion, OpenRocket is a very good tool for design and testing of model rockets.

Future Analysis

In future articles we will go into more detail in the analysis. As well we will touch on construction techniques so that our rockets will attain the highest apogee possible.

Measuring the Flight

For our flight analysis measurements we used the Altimeter Two from Jolly Logic. Altimeter Two displays flight data through the use of its LCD screen (although it charges by connecting to a USB port it does not download data to a computer). Altimeter Two is currently offered in the Sigma Rockets Online Store. For your convenience we have provided a link to purchase this device if you choose.

The Altimeter TWO is designed exclusively for model rocket flight analysis. It measures top speed, engine burn time, ejection altitude, coast time to apogee, descent speed, peak and average acceleration, apogee to ejection time and the total flight duration. Price: $68.99 CAD Display: LCD Size: 12mm X 16mm X 49mm Weight: 6.7 grams Useful Range: 15 to 9000 metres above sea level Charging: Internal battery charged by USB port

©2012 Sigma Rockets and Aerospace Inc.

Figure 1 - Flight Path of a Model Rocket

Our Test Flight

For the purposes of this article we have included data collected from our test flight with our rocket flight path graphic. This was done to further explain a model rocket flight. Our test rocket was launched using an Estes B6-4 rocket motor.

Thrust Phase

We will start our discussion with the thrust phase of a model rocket flight. This is the first phase of the flight and begins right after ignition. It is during the thrust phase where the model rocket gets all its upward acceleration. The length of the thrust phase is determined by the burn time of the motor. For our test flight the burn time was measured at 0.8 seconds.

The acceleration and maximum velocity the rocket reaches is determined by the total impulse of the motor and the weight of the rocket. And it occurs during the thrust phase. For our test flight the maximum acceleration was recorded as 89.18 m/s². The maximum velocity that our test rocket reached was 23 m/s.

Total impulse simply means the product of the average force of the motor and the burn time. In other words:

Since force is measured in Newtons and time in seconds, Total Impulse would be measured in Newton-seconds. We will not determine Total Impulse in this article. In future articles we will go into more detail with regards to this parameter.

Coast Phase

After the burn time of the thrust phase the delay or coast phase begins. It is during this phase where there is no thrust coming from the motor. It is here where the rocket begins to decelerate. It may reach its apogee during this stage. The coast phase gives way to the ejection of the recovery device. For our test flight the coast phase was broken up into two values. The first one was the time taken from the end of the thrust phase to the apogee of the flight. This was recorded as 2.45 seconds. The second time was the time taken for the rocket to go from apogee to ejection. It was recorded as 2.15 seconds. Thus the total time the model rocket coasted for before ejection was 4.6 seconds. This time is known as the delay time.

You may find the delay time in the model rocket classification as well. It is the last number shown. For example a B6-4 motor has a delay of 4 seconds which is pretty close to the actual time we recorded.

Apogee and Ejection

On our graphic in figure 1 we show the ejection charge coming after apogee or the highest altitude in the flight. This is the case for most rocket flights. This is also the most desirable flight pattern. However, in some situations the ejection of the parachute comes before the apogee of the flight. This is caused by a delay that is too short.

It may be dangerous for ejection to happen before apogee as the rocket is traveling at a high speed when the parachute is deployed. This may damage the parachute and the rocket. As well, the opposite is true. A delay that is too long may make for a deployment too close to the ground. Or in some cases so late that the rocket crashes.

For our test flight the apogee was recorded at 46 meters. Our ejection altitude was recorded at 28 meters above the ground. Apogee occurred 2.45 seconds after the end of the trust phase or 3.25 seconds after the rocket lift off. The ejection happened at 4.6 seconds after the burn phase or 5.4 seconds after the rocket left the ground.

Recovery Phase

Nothing brings more relief when launching model rockets than to see the parachute glide the rocket to a soft landing. The speed at which the rocket returns to the ground depends on the size and efficiency of the recovery device. Generally it is good to bring a model rocket down gently so that it will not be damaged. The recovery phase starts once the ejection charge is fired and the parachute is pushed out. For our test flight the rocket descended at 5.3 m/s.

Our Test Model Rocket

The test rocket we built was done using OpenRocket. The rocket has 3 fins, is 63 cm long with a 34 mm diameter. A B6-4 motor was loaded into the rocket as well as an electronic device to take measurements for our flight analysis. We used Altimeter Two from Jolly Logic for these measurements.

Flight Analysis

Our model rocket was launched on a calm day. The flight was smooth and the nylon parachute deployed as expected. We have included a table of our flight measurements below to correspond with our graphic in figure 1 above.

In the video of our flight analysis the model rocket is stopped and held in place at its various points in the flight path. As mentioned above, the measurements were taken using Altimeter Two from Jolly Logic.

Measuring the Flight

Altimeter Two displays flight data through the use of its LCD screen (although it charges by connecting to a USB port it does not download data to a computer). Altimeter Two is currently offered in the Sigma Rockets Online Store. For your convenience we have provided a link to purchase this device if you choose.

The Altimeter TWO is designed exclusively for model rocket flight analysis. It measures top speed, engine burn time, ejection altitude, coast time to apogee, descent speed, peak and average acceleration, apogee to ejection time and the total flight duration. Price: $68.99 CAD Display: LCD Size: 12mm X 16mm X 49mm Weight: 6.7 grams Useful Range: 15 to 9000 metres above sea level Charging: Internal battery charged by USB port

©2012 Sigma Rockets and Aerospace Inc.

Mercury Atlas with Friendship 7

Historic Flight

On February 20th, 1962 a highly decorated captain in the United States Marine Corps named John Glenn became the first American to orbit earth. His Mercury capsule named Friendship 7 orbited the planet three times in almost five hours before returning home.

The successful launch was at a crucial moment in the early years of the space race against their rival and other world super power the Soviet Union. Russia had already launched two cosmonauts into orbit beginning with Yuri Gagarin on April 12th, 1961 and Gerhman Titov on August 6. Titov orbited the earth for an entire day.

Meanwhile NASA in the United States had only sent astronauts Alan Shepard and Gus Grissom on sub-orbital flights. They were launched into space using the short range Redstone rocket designed by the German engineer Wernher von Braun. The more powerful Atlas rocket which would later fire Glenn into orbit was still being tested.

The Beginning of NASA

The National Aeronautical Space Administration opened its doors in October 1958 when President Eisenhower decided a civilian agency should lead the country into space. The United States Air Force and the army had been squabbling for years over who should have jurisdiction over it.

In 1957 the Soviet Union launched the world’s first man made satellite ‘Sputnik’ into orbit. Many believed Eisenhower’s wait for a non-military rocket cost the United States the glory of reaching space first. Eisenhower eventually let the army launch a modified Jupiter army rocket into orbit. This rocket named Juno 1 was designed by the famous rocket scientist Werner von Braun. The launch put America’s first satellite, Explorer One into orbit on January 31st, 1958.

JFK Chooses the Moon

By the time Glenn was preparing for his historic flight in 1962, the Eisenhower administration was out of the White House. A younger more adventurous president named John F. Kennedy took over. President Kennedy was determined to make up for all the ground he felt was lost to the Soviets since World War II had ended. JFK, as he was known, famously set his sights on the moon.

Nevertheless, before the moon could be reached the United States would first have to orbit the earth. This was going to be up to forty year old John Glenn. His Atlas rocket had experienced some highly publicized explosions since the first test flights in 1957. This made the astronauts a feel a little bit uneasy.

John Glenn climbs into Friendship 7 before his historic flight

The Mercury Seven

The Ohio native was undeterred however. Glenn had been selected in 1959 along with six other test pilots from different branches of the military to become America’s first astronauts. Glenn was the only one from the Marine Corps. The Mercury Seven, as they became known, would ride into history on-board dangerous rockets carrying thousands of pounds of explosive fuels. These rockets tended to blow up during testing more often than the engineers would have preferred. “Our rockets always blow up and our boys always botch it” was a classic line from Tom Wolfe’s novel and Hollywood movie “The Right Stuff” chronicling the Mercury Seven program.

After two months of delays and already ten scheduled launch postponements the Atlas rocket finally ascended from pad 14 at 9:07 am local time on February 20th, 1962 from Cape Canaveral in Florida. Inside the 4,265 pound Mercury capsule, named Friendship 7, was John Glenn. He squeezed himself into a custom made seat. His spacesuit was just as silvery and shiny as the rocket he was riding on. Over the roar of the three liquid fuelled engines the words Scott Carpenter’s words of “God speed John Glenn” echoed through the capsule communicator. The seventy-five foot shining aluminum rocket performed perfectly on take off. The black Mercury capsule perched on top separated as planned from the Atlas booster five minutes later. NASA was aiming for seven orbits. Things were going well early on.

John Glenn Takes Control

Soon after, however, Glenn began encountering problems. During the second orbit a thruster to help control Mercury’s attitude was not working properly. Glenn was immediately forced to go from ‘fly by wire’ to manual control. There were eighteen of these tiny thrusters around the outside of the capsule fuelled by hydrogen peroxide controlling the pitch, roll, and yaw. Glenn had to constantly make manual adjustments to the drifting space capsule causing the thruster fuel to drain faster than expected. This was vital because Glenn needed some fuel to make last minute manoeuvres for the return home. The process involved an important attitude correction making sure the heat shield was facing down and on the proper angle during re-entry. Glenn was able to manage the situation on his own through manual control. It wasn’t long however before the astronaut received more unsettling news from mission control. This time from where he was sitting there was nothing the marine fighter pilot could do about it.

Harrowing Re-entry

A flashing light on a lone panel somewhere in the control center indicated that the landing cushion had deployed and possibly loosened the heat shield. The heat shield was the last and only line of defence protecting an astronaut from the extreme temperatures faced during re-entry through earth’s atmosphere. Flight Director Chris Kraft was certain the light was a false reading and opted to jettison the retro pack as planned when re-entry commenced. On launch day the Flight Director is always in charge. On this day though, Walt Williams, the Operations Director and Kraft’s boss was standing in the back of the room and disagreed with the Flight Director’s decision.

Williams suggested the retro pack remain attached to the bottom of the capsule for Glenn’s entire way down. He argued that the same metal straps holding the rocket pack into place would also secure a loosened heat shield as well. The retro pack was hopefully going to burn up through the atmosphere without giving any problems to the capsule. The pack was usually discarded as soon as the retrograde rockets did their job and the capsule began descending from space. Kraft was concerned that if the pack was left on and there happened to be trace amounts of hydrogen peroxide fuel left over in any of the small retro engines it could cause an explosion.

There was also the worry that not all of the retro pack would burn up as planned during its descent and parts could break off and damage Friendship 7. Glenn was not happy when he heard the change of flight plan so late in the mission. It was customary in the military for a test pilot to receive any and all information regarding his troubled aircraft as soon as a problem occurred. This was not done and NASA made the decision to keep the problem from Glenn until the very last minute. It had concerned them enough they shortened Glenn’s trip to just three orbits. As well a phone call between the astronaut and President Kennedy which was supposed to take place on one of Glenn’s passes over the United States was cancelled.





To break away from orbital speed and return to earth earlier than he had wished, Glenn fired his control rockets one at a time to position the craft for re-entry. The capsule’s blunt end where the heat shield was attached received temperatures in excess of 3000 degrees Fahrenheit for several minutes. This is the black out period between the astronaut and mission control when radio signals are absorbed by the fireball surrounding the craft and communication is not possible. Through his small window Glenn witnessed charred remains of the retro-pack bang up against the sides of Friendship 7. He continued to report in to the control centre even though it was impossible for them to hear him. He was on his own and would later comment that he actually enjoyed the peace and quiet. “Cautious apprehension” were the words used by Glenn himself describing his true feelings through the anxious minutes before the drogue chute finally deployed at 22,000 feet. Mission control along with the entire country waited nervously on the ground for Glenn to report in.

JFK inspects Friendship 7

A Safe Landing

The Mercury Capsule’s massive orange and white striped main parachute sprung open above Friendship 7 at 10,000 feet over the Atlantic Ocean. Soon after the landing bag deployed on time and inflated around the capsule without any problems. Kraft ended up being right, it was a false alarm. After three orbits around the earth and back John Glenn and his Friendship 7 capsule had travelled 81,000 miles in just 295 minutes. Glenn was down to fifteen percent fuel in his manual tank when he hit the water. He had flown most of the flight on his own. Astronauts were no longer “spam in a can” as renowned World War II pilot Chuck Yeager once professed.

Friendship 7 undershot the predetermined splash down point in the Atlantic Ocean by 40 miles while ending up 800 miles south east of Bermuda. This was just 500 miles from where he lifted off from at the Cape. When the USS NOA arrived to retrieve the capsule it was gingerly bobbing up and down in the water with the American astronaut safely inside. On-board the recovery ship Glenn finally received his much anticipated call from President Kennedy with congratulations over the radio-telephone.

A Hero’s Welcome

John Glenn received a hero’s welcome on his return to the United States. When Glenn arrived in New York on March 1st over four million people lined the streets of Manhattan for the largest ticker tape parade in New York City history. Because of Glenn’s successful trip around the world and back the American space program quickly moved forward. It was now at least equal with the Soviet program. The Mercury flights would come to an end in 1963 after Gordon Cooper successfully orbited the planet twenty-two times on May 15th.

Life After NASA

Six weeks following President Kennedy’s assassination in Dallas on November 22nd, 1963, John Glenn resigned from NASA and the space program to pursue his love for business and politics. In 1975 Glenn was elected the Democratic Senator for his home state of Ohio. In 1998, at the age of 77, he flew on-board the Space Shuttle Discovery, becoming the oldest person to travel in outer space. Friendship 7 remains on display in the Smithsonian Air and Space Museum in Washington, DC. The heat shield is still firmly in place.

Fifty years later Glenn’s flight is regarded in historical ‘Cold War’ terms as the launch that put the United States back on course in the space race with the Russians. The Gemini and Apollo programs succeeded Mercury. This lead to Neil Armstrong’s legendary date with the moon in 1969.

But first it was John Glenn in 1962 and his three orbits around our planet in a Mercury capsule that paved an invisible flight path to outer space for future American astronauts like Armstrong.

“This is the new ocean, and I believe the United States must sail on it and be in a position second to none.”
-President Kennedy immediately following John Glenn’s return to Earth in Friendship 7.

About John Glenn

• Born: July 18th, 1921 in Cambrigde, Ohio
• Education: Bachelor of Science degree in Engineering from Muskingum College, Ohio.
• Glenn was commissioned in the Marine Corps in 1943.
• In July 1957 Glenn set transcontinental speed record in F8U Crusader from Los Angeles to New York in 3 hours and 23 minutes.
• John Glenn joined NASA in 1959 as part of the Mercury Astronaut Program.
• On February 20th, 1962 Glenn piloted the Mercury/Atlas 6 flight.
• In 1975 Glenn was elected Democratic Senator for Ohio.
• On October 29, 1998 Glenn flew on-board the STS-95 (Space Shuttle) at the age of 77 years old.
• On July 18, 2011 John Glenn celebrated his 90th birthday. Glenn and Scott Carpenter are the last living members of the Mercury Seven.

About the author

• Wilfred Ashley McIsaac is a graduate of the Toronto School of Business and now writes freelance articles concentrating on historical achievements in space. McIsaac has flown high-powered rockets in Canada since 1997 and recently launched a rocket in Gananoque, Ontario carrying mail addressed with 75 year old ‘First Canadian Rocket Flight’ stamps. Video of the flight was a success on YouTube and the Sigma Rockets website and may be viewed here.

©2012 Sigma Rockets and Aerospace Inc.

Figure 1 - Basic Pressure Altimeter

Using Electronic Altimeters for Model Rockets

The most common electronics device carried aboard rockets are electronic altimeters. In recent years, electronic altimeters have become more and more plentiful and as a result less expensive than when they were first introduced. As well the size of the altimeter has decreased significantly adding as little as 6 grams of weight to the rocket.

Altimeters employed in rocketry may be used to control the ejection charge. But most of all they are used to measure the apogee, or highest altitude, achieved in a flight. Simple altimeters indicate measurement through a series of beeps. Some altimeters may be connected to a computer for data extractions. Still other use a small display screen on the altimeter itself to indicate measurements taken. Figure 1 shows a simple altimeter that relays the apogee of the flight through a series of beeps.

To measure altitude either of two basic methods are employed: measuring acceleration or measuring air pressure.

Pressure Altimeters

Pressure altimeters use atmospheric pressure to determine altitude. The lower pressure high above the ground is compared to ground level in order to determine the altitude.

Sealed aneroid (defined as using no liquid) wafers are exposed to outside air and the pressure difference causes the wafers to expand or contract. This change is then measured and used to determine altitude.

Figure 2 - Installing an altimeter into an electronics bay

Pressure altimeters must measure the outside air. Thus vents (holes) must be made in the rocket or the payload section holding the altimeter. Pressure altimeters may also be affected by pressure fluctuations on rockets that reach speeds in excess of Mach 1 (the speed of sound) and low pressure caused by weather. However, modern pressure altimeters take these factors into account and adjust for it. For example, some altimeters will not measure altitudes of less than 15 meters or 50 feet to account for low pressure due to weather.

Accelerometer Altimeters

Accelerometer altimeters measure the change in velocity (the acceleration) of the rocket. By knowing this and the time, accelerometer altimeters are then able to determine the apogee of the flight.

These type of altimeters do not need to be vented to the outside air. However, they are less accurate when the rocket does not fly perfectly straight.

Dual Deployment

For bigger or high-power rockets, altimeters may be used to control the ejection charge used to deploy the parachute. Often this involves having two ejection charges fired, one for pushing out a drogue parachute and the other for deploying the main parachute. By pushing out a drogue the rocket is positioned such that it is falling horizontally. This keeps the rocket from picking up too much speed in descent and allows the main parachute to be fired out sideways and not down.

Figure 3 - Altimeter Data

Dual deployment allows for more accurate landings as the main parachute is fired at a relatively close altitude to the ground. This cuts down on drift significantly. Multiple altimeters are often used in dual deployment systems. Usually the altimeters come from different manufacturers. This cuts down on the risk of an altimeter not firing due to sensitivities based on manufacturer. Dual deployment altimeters are often installed in a separate payload bay. Figure 2 shows such an installation.

Measuring More Than Altitude

As mentioned above, some altimeters may be used to measure more than just the apogee of the flight. Some altimeters, such as the Entacore AIM USB altimeter, have USB connections that allow their data to be extracted to a computer and displayed graphically (see figure 3).

Figure 3 is a extraction of data from a rocketry flight using this altimeter. As the AIM USB altimeter is used for dual deployment in high-power rockets it may be configured for deployment times using the computer program provided.

Through the use of its small LCD screen the Altimeter Two from Jolly Logic is able to give flight measurements such as top speed, engine burn time, ejection altitude, coast time to apogee, descent speed, peak and average acceleration, apogee to ejection time and the total flight duration.

Additional uses for altimeters

Altimeters that offer more than just the altitude may often be used in non-flight applications. For example, how about taking one on a roller coaster ride! That first drop may provide some interesting data. Measuring velocity, acceleration, and height are valuable parameters to have for interesting classroom discussions.

Purchasing an Altimeter

Careful research should be taken to determine the altimeter that is best for your application. Factors such as cost, functionality and size may be considered.

In the case of dual deployment altimeters, care must be taken to choose one with a good reputation as a failure of a dual deployment altimeter could prove tragic. Quite often redundancy in the form of multiple altimeters and timers is employed in a high-power rocket to reduce the risk. We currently do not carry dual deployment type altimeters in the Sigma Rockets Online Store.

Below I have listed two altimeters, Altimeter One and Altimeter Two from Jolly Logic, that we currently do offer. Altimeter One provides a simple way to measure and display apogee of a flight and Altimeter Two offers more flight analyses as described above. These have a protective casing to cover the circuit board instead of exposing it as most altimeters do. Please note however, that despite looking like USB memory sticks, the altimeters use the USB connection merely for charging their internal batteries and do not transfer flight data to the computer. Flight data is displayed through the use of their LCD screens.

The Altimeter ONE measures peak flight altitude and may be used for rockets, planes and kites. Price: $49.99 CAD Display: LCD Size: 12mm X 16mm X 49mm Weight: 6.7 grams Useful Range: 15 to 9000 metres above sea level Charging: Internal battery charged by USB port	The Altimeter TWO is designed exclusively for rockets and measures top speed, engine burn time, ejection altitude, coast time to apogee, descent speed, peak and average acceleration, apogee to ejection time and the total flight duration. Price: $68.99 CAD Display: LCD Size: 12mm X 16mm X 49mm Weight: 6.7 grams Useful Range: 15 to 9000 metres above sea level Charging: Internal battery charged by USB port

©2012 Sigma Rockets and Aerospace Inc.

Weather Balloon - NASA image

What are Weather Balloons?

Also known by the name “sounding balloon”, weather balloons are unmanned high altitude balloons filled with helium or hydrogen that float up into the stratosphere (18 to 37 km above Earth) in order to measure atmospheric pressure, temperature, humidity and wind speed.

Devices such as a radiosonde often accompany the balloon on its flight to record atmospheric parameters, radar and GPS may be used on the balloon as well to measure things like wind speed.

Weather balloons have been in use since 1896 when French meteorologist Léon Teisserenc de Bort started launching them from his observatory in France. His experiments would lead to the discovery of the stratosphere, the second major layer of Earth’s atmosphere.

The $150 Space Flight

More and more teams from all around the world are using weather balloons to float payloads into near space. As digital photographic and GPS technologies continue to improve and become less expensive, constructing a payload to send aloft in a balloon has become a reality for many.

A team of MIT students have set up a website outlining the steps to make a $150 flight into the stratosphere or near space. The link for this flight may be found here: http://space.1337arts.com/.

According to their website, 1337arts.com, the group is “dedicated to celebrating the marriage of art and science and promoting the beauty of scientific art”.

Embedded Video

Released only 2 days ago the video on the Lego Man’s rise into space already has over 630,000 views on YouTube as of the writing of this article.

On behalf of Sigma Rockets I would like to congratulate Mathew and Asad on their picture perfect flight and their place in the history books of aerospace exploration.





©2012 Sigma Rockets and Aerospace Inc.

Sigma Rockets High Power Rocketry Website

High Power or Model

The run up to the moon landings were certainly an exciting time for space travel and rocketry. In the late 1950s the hobby of model rocketry was born out of the need to provide safe rocket motors to a general public eager to produce budding rocket scientists.

Those that grew up with rocketry would discover in the late 1980s the rise of high power rocketry where motors sizes increased significantly. Similar to model rockets, high powered rocketry offered greater size rockets and larger payloads.

Initially high powered rockets were brought down to Earth using the same ejection charge following thrust and delay method but would soon incorporate timers, altimeters and other systems to recreate the flight of a model rocket but in a much bigger size. The complexity, plus the risk in launching much bigger rockets, resulted in the creation of new types of rocket clubs such as Tripoli.

What can be found on the new website?

We have combined articles geared specifically towards high power fliers and an eCommerce store for high power rocketry motors. For high power rocketry accessories and rockets we are currently still offering them on our main eCommerce website located here: www.sigmarockets.ca.

We will change this in the future so that everything associated with high power rocketry may be found on the new site.

New product layout

Most high power rocketry fliers know what products they’re looking for, and to facilitate this the items on the new site are laid out in table formats. Motors are sorted from smallest to biggest and in the case of Cesaroni motors, broken down into subsections based on diameter size.

What will become of the existing websites?

Our move to a separate high power website will allow us to serve non high power customers better through our main eCommerce website and the Articles website where you are reading this article from. Articles that pertain to rocketry and aerospace in general will still be hosted on this website.

Your Feedback

As always we appreciate any comments or suggestions on how to make Sigma Rockets better. If you have any suggestions please do not hesitate to contact us by using our contact form located here.


©2012 Sigma Rockets and Aerospace Inc.

OpenRocket

The ability to design and test your rocket before actually building it is quite the asset for the rocket designer. Many programs exist for this. One of these programs is the Java-based open source software named OpenRocket.

About OpenRocket

OpenRocket features realistic wind modeling, clustering and staging, just to name a few. It allows for free-form and canted fins. OpenRocket is an Open Source project licensed under the GNU GPL.

This means that the software is free to download and to use for whichever purposes you desire. You do not need to purchase or register for a license code to use this software.

As well the source code is also available for studying and extending. So for those of you that are Java programmers, OpenRocket source code may be downloaded and modified to suit your purposes.

Downloading and Running the Program

As with many software programs the best way to learn it is to give it a try. You may download OpenRocket from the download page here.
OpenRocket is hosted on the SourceForge network and you may visit the website of OpenRocket by clicking here. To use the software download the latest version and double click on it. It will come as a jar file. You will need the Java runtime library installed on your computer. You may download java from the java.com website by clicking here.

You may run OpenRocket on Windows, Linux, Mac OS X or any other operating system that supports the latest Java Virtual Machine. For those of you using Mac OS X you may not need to download Java as the latest version should be installed with the Operating System.

Please note however I was not able to run OpenRocket on a G4 Mac running Leopard. I didn’t have a problem with an Intel based Mac running the same OS. This is due to the fact that the version of Java needed for OpenRocket (the latest version) is not available for non-Intel Mac computers.

Getting Involved

As OpenRocket is an open source project there are opportunities to get involved with the development, testing and documentation of the program. As of this writing the project is currently looking for Java Developers, people to assist with aerodynamic computation methods and people to help write the documentation. Getting involved would be an excellent way to not only improve the program but to help you in your aerospace education.

For more information on OpenRocket please visit the website at: http://openrocket.sourceforge.net.

©2011 Sigma Rockets and Aerospace Inc.