Ross Millikan
  • Member for 8 years, 6 months
  • Last seen this week
  • San Mateo, CA, United States
Why was the Shuttle's LOX tank on top of the LH2 tank, since that makes it more top-heavy?
Accepted answer
25 votes

While in the atmosphere, a forward center of gravity contributes to stability. You want the center of gravity to be forward of the center of pressure for aerodynamic stability. A longer distance ...

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Why is it not possible to deorbit in a shallow glidepath?
16 votes

When you reenter at a shallow angle your velocity is almost horizontal and you have orbital velocity. A small amount of lift will lift your velocity above the vertical and send you back into orbit. ...

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Is it bad if hydrazine freezes on a spacecraft? Is it always kept as liquid, or can it be safely allowed to freeze and then thawed when needed?
14 votes

The Olympus satellite (1989-053A, 20122) lost pointing and power for long enough that all the fuel froze. It was recovered after a couple months and the fuel defrosted. I couldn't easily find what ...

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Why are Curiosity's wheels aluminum rather than titanium?
13 votes

Aluminum is less dense than titanium. For the same mass, the 0.75mm thick aluminum would have to be replaced with 0.45mm thick titanium. Although the titanium sheet would be stronger in tension, it ...

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Do solar panels on satellites gather dust and need cleaning?
10 votes

Satellites do not have any capacity to clean the solar arrays. The solar arrays degrade over life due to many factors: radiation damage, UV darkening, micrometeroids, etc. The manufacturers have ...

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Would a flywheel energy storage have a distinct advantage or disadvantage in zero or low gravity?
10 votes

You are correct that flywheels can be used for energy storage like batteries. As with all engineering trades, this comes down to many factors: mass, cost, efficiency, lifetime, reliability ... ...

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How much do eccentricities of different satellites in GSO vary?
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8 votes

Once in GSO, the eccentricity is perturbed by a few effects, particularly the pressure of sunlight (not the solar wind), on the satellite. It accelerates the satellite at 6PM local and decelerates ...

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Do spacecraft ever release unneeded gases into space?
7 votes

Section 30.4 of this NASA document describes passivation of spacecraft at end of life. The objective is to remove all sources of stored energy including pressurized gases and the way to do it is to ...

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Do any launches bypass LEO?
6 votes

You can't launch straight to Geostationary Orbit (GEO) as you can't get the perigee high enough without a burn at geosynchronous altitude. The Proton has done that, though with a Low Earth Orbit (LEO) ...

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Could I home-brew my own rocket fuel?
6 votes

What is your objective? For many purposes, any hydrocarbon will suffice. Gasoline and diesel are quite available. RP-1 has longer chains, which means more carbon per hydrogen and a higher boiling ...

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Why don't reaction wheels destabilize spacecraft over time?
5 votes

Reaction wheels can store angular momentum up to a certain limit. If you Fourier analyze the torques on the satellite, some are constant and some are sinusoidal. The reaction wheels can store the ...

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How much fuel would be required to send a 300g satellite to space using Rockoon?
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5 votes

Randall Munroe in his What If book says it well: The reason it's hard to get to orbit isn't that space is high up. It is hard to get to orbit because you have to go fast Being $32$ km higher ...

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What kind of mission objective would make a parabolic escape trajectory desirable?
4 votes

I can't think of one. For mission planning there is nothing special about parabolic velocity. There is something special from the perspective of teaching orbital mechanics as it is the boundary ...

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What is the largest body in the solar system we could meaningfully and accurately adjust the orbit of?
4 votes

The phrase "2015 tools and knowledge" combines two very different things. If we are limited to today's tools, the best we can do is impact a body so the body absorbs the momentum. The easiest way to ...

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Can a launch-provider determine from the flight-profile whether the payload will be in the wrong orbit?
4 votes

The simple answer is yes. Arianespace was asked to deliver the satellites to a given separation orbit. They track the rocket, so have data that tells what orbit was achieved. They provide the ...

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Why do many Mars missions launch now, if the Hohmann transfer orbit is the most propellant-saving one?
3 votes

Much of engineering is about compromises. One can find an ideal solution, like a Hohmann transfer orbit. Yes, that is the most fuel efficient way to get from earth orbit to Mars orbit. It is like ...

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Orbital Rendezvous vs Hohmann Transfer
3 votes

The basic idea is that if you can get there within a small fraction of the orbit, the orbital dynamics do not matter at all. You are close enough that the two spacecraft will essentially be in the ...

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Will crewed vehicles ever follow multi-flyby trajectories?
3 votes

Mission design is very hard because it has so many different constraints. Finding the path to solar escape with minimum delta v within a given calendar window is well defined and will probably have ...

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Why are so many space telescopes placed in LEO instead of at Lagrange Points? And why do we hear about Hubble more than any Langrange-orbit telescope?
3 votes

Each telescope has a mission or several. The selection process balances the expected scientific benefits with the cost. Although this balancing is far from perfect, the fact that it takes more delta ...

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How did SES-9 reach geostationary orbit from inclined transfer orbit (from F9 2nd stage)
3 votes

GEO and GSO are synonyms for geostationary (earth) orbit. They are orbits that are in the equatorial plane at an altitude that has a $24$ hour period so that the satellite appears to stay at one ...

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What's stopping space probe communication from being jammed?
3 votes

Jamming the downlink signal is quite easy. It is extremely low in power, so if you just set up a signal source in the vicinity of the receive antenna, there will probably be enough off-axis gain that ...

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How are rockets tested (hot fire)?
3 votes

The effect of external pressure on a rocket engine is backpressure at the exit plane of the nozzle. The combustion chamber is well insulated from that by the sonic flow at the throat o the nozzle. ...

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Would it have been cheaper and/or faster to put a James Webb-like Space Telescope on a balloon instead of a rocket?
2 votes

The place to start is by listing the science objectives of the mission. Balloon telescopes can be much less expensive than satellite borne ones, but the design of a satellite borne one allows a much ...

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How closely spaced are satellites at GEO?
2 votes

Some satellite operators intentionally locate more than one satellite in a single orbital slot. They employ a stationkeeping strategy to keep them physically separated. Minimum distances of a few ...

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Specifying a position and velocity of body in a Kepler simulation
2 votes

You can do both. For each object, store the time of perihelion. You have a global time for observation. A subtraction gets the time since perihelion.

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What is an approximation of how much silver could exist on the moon?
Accepted answer
2 votes

This Wikipedia page shows the abundance of silver on earth as $50$ parts per billion by mass. One could assume that the moon is not too far off that. Multiply by the mass of the moon $7.3477 \cdot ...

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Dragon RCS: Four controlled degrees of freedom... or six?
1 votes

Each thruster will have a thrust vector. That can be resolved into torque and translation depending on the CM. If you have six thrusters you should be able to get all six degrees of freedom. If you ...

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Why do artificial satellites need orbit correction, but natural ones don't?
1 votes

The important thing is that artificial satellites have a function that often requires the satellite to be in a specific orbit. Keeping it in that orbit requires correction. Many artificial satellites,...

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How are accidents involving rockets and space vessels investigated?
1 votes

The process is like any other careful investigation. You gather all the data you can. Here it includes documentation of the build of the equipment, test data along the way, telemetry during the event....

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Lunar-built Spacecraft
1 votes

The advantage of building on the moon is that it is a shallower gravity well than earth, so requires less propulsion to get to Mars (or elsewhere). The major disadvantage is that (for the foreseeable ...

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