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Aerospace & Aviation

¨  How do you accomplish making a rocket soar?
¨  How are rockets compared to the speed of sound?
¨  Why does ice form on the outside of rockets?
¨  What propellants should I use for my homemade rocket?
¨  Did Auk XXXI break the sound barrier?
¨  Which speed of sound reference is used during a rocket launch?
¨  When do the Delta II boosters ignite?
¨  What is venting from the Delta II booster stage?
¨
  Precipitation on the Delta rocket camera during Mars launch
¨
  Why do we use nautical miles in spaceflight?
¨  How do the Delta II booster rockets jettison?
¨  How are calculus and differential equations applied to rocketry?

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QUESTION:
How do you accomplish making a rocket soar?

ANSWER from Mike Bastoni on 22 September 2005:
Hi...it's certainly easier to make a rocket soar then it is to make a Dinosaur......I had to write that, it just seemed like too much fun.

I think another way to make a rocket sore is to smack it on the booster with a launching pad...oh oh, I'd better quit now with the humor.

Any way I'm not exactly certain what you mean...but if you're asking how to make a rocket fly...that's fairly easy.  Here is an experiment you can do to get a sense of how a rocket engine moves a rocket.

Ask your phys-ed department for a small to medium size medicine ball or weighted exercise ball.  Sitting on a skateboard (remember sit don't stand) try and throw the weighted exercise ball as hard as you can in the direction you are facing...if all goes well the ball will move away from you and you will move in the opposite direction away from the ball...

If the skateboard had perfect wheels and bearings, with no frictional forces acting on them, the product of the balls mass x the velocity it was thrown at, would be equal to the product of the mass of you, and the skateboard times the velocity that you move away from the ball.

Rocket engines work in a similar fashion...hot, presurized gases exit the rocket engine nozzle.  Although the hot pressurized gases have very little mass...they exit extremely fast.

The product of their relatively small mass, times their relatively high velocities creates a force we call thrust.  The thrusting force is described by a measure we call the total impulse.  The total impulse is the product of the thrusting force (measured in lbs or Newtons) times the burn time of the engine.

It is this total impulse that gets the rocket up to speed.  With model rockets the burn time is very short, on the order of .3 - 1.2 seconds on average and the maximum thrust force is around 3-8 lbs.  On the shuttle, the burn times are many times longer and the thrusting forces are insanely high.  Somewhere in the order of 3 x 10^7 pounds for the main engines and boosters combined.

Here is a link to a web site with a great rocket altitude prediction simulator...I use it in class every year.

http://webalt.markworld.com/webalt.html

We use it to play rocket golf.  A game where we try and land rockets with specially modified Estes A8 rocket engines inside hula hoops at ranges of 200 - 300 feet!

Hope this helps to get you thinking about rockets...spend some time tonight cruising the web and using search engines like Google and Yahoo and keywords like rocket engines, rocket thrust, and space shuttle thrust..

Enjoy

Mike Bastoni

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QUESTION:
How are rockets compared to the speed of sound?

ANSWER from Homer Hickam on 1 September 2005:
I believe you are asking whether rockets can go as fast as the speed of sound which is around 700 miles per hour.  The answer is yes and some rockets can go much faster.  For instance, rockets that put satellites into orbit go 25 times faster than the speed of sound!

But not all rockets have to go fast.  Some rockets, such as those used for fireworks during celebrations, go very slow.  You can even watch them from launch all the way until they shower the sky with sparkles.  You should also look up how sound works and why it goes as fast as it does.  For instance, do you know that sound goes faster in water than it does in the air?  You should ask your science teacher to explain sound and sonic waves to you.

Homer Hickam

[Editor's Note: Be sure to read some of Homer’s books about rockets including: The Rocket Boys, The Coalwood Way and Back to the Moon.  The first two are memoirs; the last one is a fictional story.]

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QUESTION:
In the movie Apollo 13 when the rocket takes off, ice chunks are seen falling off.  The movie takes place in Florida where it is at least 80 degrees F so where did this ice come from?

ANSWER from Dean Davis on 16 February 2005:
The Apollo Saturn V rocket used a cryogenic (super cold) mixture of Liquid Hydrogen (LH2) propellant & Liquid Oxygen (LOX) oxidizer as its rocket fuel, like the Space Shuttle External Tank (ET).

This rocket fuel is much colder than outside ambient (normal temperature) air, so it tends to condense on the outside of the rocket (like water droplets on the outside of a Coke can after taking it out of the refrigerator on a hot day).  This typically occurs near fueling vents where it turns to frost and ice.  During liftoff, these chunks of frost and ice fall off.

It is currently believed that this ice problem combined with poorly designed foam insulation on the outside of the Space Shuttle External Tank resulted in damaging the Columbia's forward wing edge Thermal Protective System and caused the destruction of the last Shuttle during reentry into the Earth's atmosphere.

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QUESTION:
I am interested in rockets, electronics, robotics, physics and computers.  I have done some simple projects in robotics and they are capable of launching simple rockets, but the rockets are not working well.  One day one exploded and I got injured.  I want to know about easily available propellents for making small rockets.

ANSWER from Dean Davis on 9 October 2004:
While I strongly encourage you to continue your rocket experiments, I suggest that you work in partnership with an experienced, responsible, adult partner and that you employ the utmost safety.  Make sure your launch site is away from air traffic, and a safe distance from homes, schools and businesses.  It really concerns me that your rocket exploded and you got hurt.

I highly recommend that you use commercial rocket engines and rocket kits available from most hobby shops.  Estes Model Rockets (www.estesrockets.com) is one of the most experienced and well known companies in this field.  You can purchase a 24-rocket engine Blast-Off Flight pack from them and experience a full day of rocket launches without worry about the rocket exploding and hurting you.

Dean Davis
Senior Principal Scientist/Engineer
Boeing

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QUESTION:
This afternoon I just finished Rocket Boys. I love it!  I think it is amazing that you got all that help from residents of Coalwood.  I'm just curious, did Auk XXXI break through the sound barrier?   I'm also amazed that you could make such a powerful propellent out of zinc dust and pure alcohol.

ANSWER from Homer Hickam on 25 September 2003:
Thank you for your note.  If you liked Rocket Boys, you're in luck.  There are two more books in what I call the Coalwood Trilogy.  The Coalwood Way is another story of the Rocket Boys, a Christmas story, that I left out of the first memoir.  Sky of Stone is the true sequel to the book.  It is being developed into a Hallmark Hall of Fame television movie but I recommend reading the book.  Books are always better than movies.  As to your question on the last Auk, it did indeed go supersonic less than a second after launch.  Zinc dust and sulfur with an alcohol binder is a very powerful propellant if you know how to handle and pack it.  The secret to our success in rocketry, however, were the finely machined DeLaval nozzles produced by the mine machine shop experts that were then lined with a ceramic coating.  As for a career path, I like to say I wanted to be an engineer but I HAD to be a writer.  Thank goodness, I got the chance to follow both passions.  For more information on all this, check out
http://www.homerhickam.com/

Homer Hickam
Retired Aerospace Engineer
Writer
Alabama, USA

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QUESTION:
When the Delta reaches "Mach 1", what is the Mach number relative to?  Since Mach is defined as v(object)/v(speed of sound), which speed of sound is the rocket velocity using?

ANSWER from Dean Davis on 4 August 2003:
The term Mach is a measure of speed with respect to the speed of sound.  760 mph is the speed of sound (Mach 1) at Standard Temperature and Pressure (STP) (32 degrees F at sea level), while at 40,000 ft and the same temperature the speed of sound is 660 mph.

The speed of sound is a relative measure named after the Austrian Physicist Ernst Mach who measured sounds speed in various mediums, temperatures and pressures.  Sound moves faster in higher density mediums such as water than in lower density mediums such as air.  Air which is the medium of interest in the Delta case is just the earth's standard atmosphere.

Dean Davis
Aerospace Engineer
Boeing
Washington, D.C.

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QUESTION:
When MER-B launched on July 7th, the countdown went to T-7 and halted.  I thought that the booster rockets had started to ignite when the countdown was halted.  It might have been my imagination as I was anticipating seeing them fire.  So, my question is, at what point in the countdown do the booster rockets on the Delta II ignite?

ANSWER from Dean Davis on 2 August 2003:
Delta Boosters use solid propellant, which cannot be shut down once they are started and they ignite at T-Zero, liftoff.  So, it probably was your imagination, for once the boosters lift-off the Delta either launches or explodes.

Dean Davis
Aerospace Engineer
Boeing
Washington, D.C.

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QUESTION:
Watching the MER-B rover launch on TV, I saw these white jets of smoke emanating perpendicularly from the booster stage of the Delta II during tanking procedures through till launch.  What is being vented out?  Is it a deliberate jetting or does the wind just making it stream out that way?

ANSWER from Dean Davis on 13 July 2003:
The venting you observed on the Delta 2 was probably caused by condensation from the Liquid Oxygen (LOX) oxidizer which is loaded into the first stage.  This oxidizer provides oxygen to the RP1 fuel for this stage.  Because the LOX is much colder than ambient air temperature it condenses with air on contact during fueling and forms harmless water vapor.

It just looks like deliberate jetting, it is just natural venting of condensation.  If it is not properly vented the resulting condensation will result in a thick layer of ice forming on the outside of the launch vehicle, which could be very bad.

By the way, these super-cold cryogenic oxidizers and fuels which are used on the Atlas, Space Shuttle, Centaur Upper Stage and certain Delta stages are not used on most launch vehicles.  Solid-propellent rocket engines have their oxidizer embedded in their fuel mixture grains, whereas other liquid-chemical rockets, such as the Titan use highly-toxic hypergolic monomethyl hydrazine & dimethyl tetroxide fuel and oxidizer combinations which ignite upon contact.

Dean Davis
Aerospace Engineer
The Boeing Company
Washington, D.C.

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QUESTION:
During the launch of MER-A, at about T+15 through to T+30 seconds, there appeared to be a splattering of a liquid onto the onboard camera.  Was that bychance the rocket going through the clouds?

ANSWER from Omar Baez on 27 June 2003 on NASADirect!:
No, what we have is, if you notice the Delta II rocket before we tank it, it is actually a nice teal blue color.  When we tank it, it turns a nice white frosty color, and there's a reason for that.  We load the first stage up with liquid oxygen, which is at minus 300 degrees Fahrenheit, and we form a frost coating over the first stage, or ice actually.  If you look at the tape when it rolls initially, right at launch, you will notice a lot of ice coming off.  What's going on in that first couple of seconds is, as we're rising, some of that frost on the launch tank is melting off and that is the precipitation you see forming on the lens of the camera as it came over the fairing on the first stage camera.

Omar Baez
Launch Director
Kennedy Space Center
Florida

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QUESTION:
How far into a mission is a spacecraft's distance calculated in "nautical miles"?  What is the reason for using the nautical mile?

ANSWER from Dean Davis on 27 April 2003:
Nautical Miles are used by NASA because pilots and astronauts have used this measurement in aviation since the Wright Brothers and this measurement originally came from sailors who used it to navigate the seven seas.

Dean Davis
Aerospace Engineer
The Boeing Company
Washington, D.C.

ANSWER from Bob Raab on 28 April 2003:
Since it has been many years since I studied navigation in college ROTC I had to search the web.  I could put the answer in my own words and impress you with my brilliance, but I'll be honest and give you this link.  See "nautical mile" at:
www.unc.edu/~rowlett/units/dictN.html

Bob Raab
Retired Airline/Former Fighter Pilot
Southern California

ANSWER from Bob Mase on 21 May 2003:
For the interplanetary missions that JPL flies, we do not use nautical miles at all.  Only the launch vehicle contractor does to describe the flight of the launch vehicle.  Once the spacecraft is separated from the launch vehicle (about an hour after launch), the spacecraft is on an interplanetary trajectory, and no one uses nautical miles past that point.  The use of nautical miles is just an historic carryover from sea and air travel.

For more info on what a nautical mile is refer to: http://www.howstuffworks.com/question79.htm

Also try: http://www.unc.edu/~rowlett/units/dictN.html

Bob Mase
Mars Odyssey Navigator
Jet Propulsion Laboratory
California

ANSWER from Omar Baez on 7 June 2003 on NASADirect!:
That was a good one! I had to go do some research on that one and I spent some time doing that.  The reason we do it - humans are lazy.  And the Earth is composed mostly of bodies of water.  And the way most charts have been written down, has been a system of Mercator projections, that means latitude and longitude.  And the way that is broken up is into squares over the Earth, a matrix of squares.  Each one of those points inside of those squares are divided into hours, degrees, minutes, and seconds.  And one minute in that Mercator projection system is equal to 60 nautical miles.  So the reason we use that is the charts are available, it's a system that's been used for many years, all the folks doing navigation over the oceans have been using it, the aviation industry uses it.  And it was just easier to adopt, and that's why we use it.  But you could really use any other system - you'd just have to chart things in that other system that you chose.

Omar Baez
Launch Director
Kennedy Space Center
Florida

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QUESTION:
When the Delta II rockets release the booster rockets, are first 3 ejected and then the remaining 6 or are they released 3 at a time?

ANSWER from Omar Baez on 7 June 2003 on NASADirect!:
I've got to take you back a little bit.  The lights - there's nine solid rocket motors on the Delta II.  We light six of them on the ground.  As we're going through the atmosphere, we will expend those six solid rocket motors.  Towards the end of its life, we'll light the other three, making that total of nine.  One second after those last three are lit, we'll jettison three of the rockets.  One second later, we'll jettison three more of them.  And during this time, we'll be still flying on three of the air-lit solids for the next 65 seconds after that point and then we'll jettison those.

Omar Baez
Launch Director
Kennedy Space Center
Florida

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QUESTION:
How are calculus and differential equations applied to rocketry?

ANSWER from Dean Davis on 15 June 2003:
Calculus & Differential Equations are used continuously in rocketry to perform a wide variety of calculations which require far more power than Alegbra and Geometry alone provide.  Some of the many rocketry problems which require these mathematical techniques include propulsion analysis (which predicts and computes rocket engine and fuel consumption), trajectory analysis (which predicts and computes launch vehicle & spacecraft flight paths, downrange stage impact sites, and reentry footprints), and astronautics analysis (which predicts and computes orbital transfers).

Dean Davis
Aerospace Engineer
Washington, D.C.

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Last Updated:
15 October 2005
 

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