Built on Facts

That Professor Goddard, with his ‘chair’ in Clark College and the countenancing of the Smithsonian Institution, does not know the relation of action to reaction, and of the need to have something better than a vacuum against which to react – to say that would be absurd. Of course he only seems to lack the knowledge ladled out daily in high schools.
- New York Times, January 30, 1929

Further investigation and experimentation have confirmed the findings of Isaac Newton in the 17th Century and it is now definitely established that a rocket can function in a vacuum as well as in an atmosphere. The Times regrets the error.
- New York Times, July 17, 1969

Which isn’t to say that the Times was entirely wrong. A propeller airplane pushes the atmosphere around itself backwards, and thus propels itself forward. A jet aircraft does the same. So does your car, which pushes the road back while the road pushes itself forward. (The earth is very massive, and is not displaces much by your car.)

Rockets are no exception. If they wish to be pushed forward, they have to have something to push backward. Basic conservation of momentum. The Times was wrong in that rockets do have something better than the vacuum to push against: their rocket fuel. In essence a rocket engine shoves the fuel back out of the rocket, and that push in turn send the rocket forward.

I say all this because several of the great pioneers in rocketry like Goddard and von Braun were not always professional well-funded research scientists. They started as curious amateurs. The tradition continues apace today. Last Saturday a man named Steve Eves lauched a 1/10 scale Saturn V rocket. The rocket was of his own construction and cost him about $25,000 – half of that being fuel costs.

It’s a thing of beauty:

Impossibly cool.

Comments

#1 joemac53
April 29, 2009

What a great treat! I am a Clark U alum, and I did my student teaching at the high school Goddard attended (the same building)! His widow was a Clark trustee for many years. The library is named for him, and his old office/lab is like a shrine on campus.

Hats off to Mr. Eves!
#2 Sarah
April 29, 2009

Some day, when I finish this graduate degree I’m working on, I will work for NASA, and contribute to space flight.

Some day.
#3 Tom
April 30, 2009

I love how it took until the launch of Apollo 11 for the Times to acknowledge that Newton’s laws are correct.
#4 Uncle Al
April 30, 2009

Suppose there were something interactive in the vacuum. (Could be – vacuum has permeability and permitivity; Casimir effect.)

http://www.igf.fuw.edu.pl/KB/HKM/PDF/HKM_027_s.pdf
3.5 megabytes
pdf pp. 25-27, calculation of the chiral case.

Take a single crystal cylinder of quartz, its long axis being the crystallographic c-axis. Spin it about the c-axis. You have a vacuum propeller.

Take two such cylinders of quarts in enantiomorphic space groups P3(1)21 and P3(2)21. Separately suspend them from filaments as bobs in a vertical vacuum torsion balance. If there were something interactive in the vacuum they would torque in opposite directions as the Earth inertially spun about its axis and gravitationally fell about the sun. Somebody should look.
#5 hedberg
May 1, 2009

A propeller airplane pushes the atmosphere around itself backwards, and thus propels itself forward.

A propeller is a rotating wing. Isn’t it better to say that the plane moves forward because of the Bernoulli principle rather than because the propeller pushes air backwards?

How about a close hauled sailboat? It moves forward because of the same physics that causes a propeller to move a plane. It’s not easy for me to visualize what the sail might be pushing against.

I understand that, given the laws of physics, it may be possible to explain either the sailboat or plane in terms of pushing against something, but it doesn’t seem to be the most straight forward explanation.
#6 CCPhysicist
May 2, 2009

Non-science nonsense like the 1929 Times article still remains. I saw a program yesterday about the Stennis test center you featured a few weeks ago, and it said (gasp) that the curved deflector that sends the thrust out horizontally across the water was there so the engine would not move vertically. Seriously bad. I think it was on the Science channel, and concerned maintenance and testing of the Shuttle main engines.

I’d nit pick that it is the atmosphere that pushes the plane forward (and the road that pushes the car forward). Your use of “itself” is a bit vague.

Even if hedberg @5 is correct about the mechanism, arguing that the air pulls the propeller forward, the reaction to this is that the propeller pulls air backward. One way or the other, you will have a large amount of momentum carried one way by the air if you want to have a large amount of momentum carried the other way by the aircraft. Stand behind a Cessna if you have any doubts about this fact!

What the Times missed in 1929 is that a rocket carries its atmosphere with it. The rocket reacts against the combustion gasses in its engine chamber, not against the ground or the air or a vacuum.
#7 Dave
May 3, 2009

If you visit the Pakachoag Golf Course in Auburn, MA, out in the middle of the 9th fairway (I think that’s where it is; it’s been quite a while since I’ve been there), you’ll find a small obelisk with a plaque that says this is where Goddard did a number of his experiments in rocketry.
#8 opony szczecin
May 4, 2009

russian rockets are the best
#9 bamad
November 6, 2010

i want to learn more about
huge and also the first