28 votes

How dangerous is tossing equipment off the ISS?

tl;dr It's not dangerous or they don't do it. As you might expect, this gets studied to death before it happens. Anything planned to be jettisoned or deployed from the ISS or any ISS Visiting Vehicle ...
Organic Marble's user avatar
10 votes

Exactly how "Ferrari-like" was GOCE? Was its drag coefficient as low as the car's?

The ion propulsion was run continuously to compensate for drag immediately. The drag force varied strongly during each orbit (i.e. changing from night to day), typically between 4 and 12 mN on its 1 m²...
asdfex's user avatar
  • 15k
8 votes

How fast do optical surfaces get dirty or damaged in space?

In addition to the space weathering phenomenon described by ebv, optical surfaces can and do get dirtied by other mechanisms as well. In particular, outgassing from the rest of the spacecraft and ...
Terrance Yee's user avatar
  • 2,264
6 votes

Exactly how "Ferrari-like" was GOCE? Was its drag coefficient as low as the car's?

Roughly how much lower was GOCE's drag compared to a typical spacecraft, or to a sphere of the same mass. Did it have a drag coefficient as low as a real Ferrari? GOCE's drag coefficient was higher ...
David Hammen's user avatar
  • 73.8k
5 votes

What's the lowest altitude that an ion engine has been used for a significant orbital maneuver?

JAXA's Tsubame satellite is planned to orbit to altitudes as low as 180 km, using an ion engine to reboost. It was launched in January 2018 into an initial orbit at ~480 km, its orbit will be ...
Hobbes's user avatar
  • 127k
5 votes

How to calculate the lowest possible altitude a satellite can orbit at due to aerodynamic heating if provided with a sufficient propulsion system?

Following @JCRM's lead: rocket horsepower questions to the rescue! See this answer and this answer for derivations and explanations. Power If we assume that most of the kinetic energy of the air ...
uhoh's user avatar
  • 149k
5 votes

What "unique control system" modulated GOCE's thrust to compensate for variable atmospheric drag? How did it know how to modulate it?

The EO Portal page on GOCE provides a lot of information and references, including for the Drag Free and Attitude Control System (DFACS). It includes this block diagram: (source; credit: Thales ...
Ludo's user avatar
  • 14.2k
5 votes

Could you skim along the Karman line using a parafoil?

Using a naive lift calculation at 100km runs into several issues. As you go above about 50km your mean free path for the atoms in the atmosphere is becoming long enough that you no longer have a '...
GremlinWranger's user avatar
4 votes

For using the acceleration due to drag formula, which coordinate frame should the satellite's position and velocity vectors be in?

First things first: A real force is the same vector in all frames of reference. All that's needed is a transformation. It's only fictitious forces that change drastically between frames. For example, ...
David Hammen's user avatar
  • 73.8k
4 votes

Does it count as orbital flight if one reentered the atmosphere due to its drag after about 1 revolution?

There is a gray area here, but probably yes. If it were called a "suborbital flight" the assumption would be that the orbit's path would intersect the surface of the Earth. Since the perigee ...
staticvoidliam7's user avatar
4 votes

What factors would contribute to a spacecraft's ability to maintain a very low orbit (VLEO) or at least orbits with very low perigees?

The lower the orbit, the higher the drag. Since the drag force is roughly proportional to area, but the resulting acceleration is force divided by mass, then the denser the spacecraft, the less it ...
Ryan C's user avatar
  • 7,852
4 votes

How exactly does atomic oxygen cause problems for spacecraft in VLEO?

It literally eats away at surfaces made of certain materials. It's pretty crazy. According to Space Mission Analysis and Design ("SMAD", 3e, by Wertz and Larson), Atomic oxygen (which I'll call ATOX ...
Michael Stachowsky's user avatar
4 votes

How low is VLEO? (FCC's newest approval for SpaceX)

Per Space News, reviewing the applications, VLEO in this context is below 350 km orbit. Of the four, SpaceX is by far the largest with 7,518 satellites constituting what it calls a “very low Earth ...
geoffc's user avatar
  • 79.2k
3 votes

Have spacecraft ever dipped below the Karman line and then safely continued spaceflight?

I've been able to find a few rocket bodies and payloads that have done so, at least for some period of time prior to decay. These objects might have been in a state of decay prior to entering in these ...
PearsonArtPhoto's user avatar
  • 121k
3 votes

What technologies enable or at least help satellite operation in Very Low Earth Orbit (VLEO)?

Yes, there are a number of different technologies that I'm aware of that are being developed specifically to enable and assist satellites in operating sustainably in lower altitude orbits. The ...
nhcrisp's user avatar
  • 76
2 votes

What is Direct Simulation Monte Carlo and why is it a good method for simulating spacecraft drag in VLEO?

My understanding is that the "Direct Simulation" part refers to the fact that rather than solving equations governing the flow (as in Computational Fluid Dynamics) it directly simulates the ...
Rustony's user avatar
  • 56

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