fernibble t1_jc7n8tp wrote on March 14, 2023 at 5:10 PM

> The deorbit vehicle shall be capable of providing at least 47 m/s of delta-v for the ISS at 450,000 kg mass.

Very interesting that only 47 m/s of delta-v, at a minimum, is needed. The orbital speed of the ISS is about 7660 m/s.

Pharisaeus t1_jc7rbal wrote on March 14, 2023 at 5:36 PM

This is because atmosphere does most of the job, you just need to drop the perigee low enough.

Consider that the Space Shuttle had around 300 m/s of delta-v available for their orbital operations. Deorbit burn of visiting spacecraft to the ISS are around 130-150 m/s.

sometimes-wondering t1_jc82g7v wrote on March 14, 2023 at 6:45 PM

Makes me think of how wasteful I am in KSP

banned_in_Raleigh t1_jc8em9b wrote on March 15, 2023 at 1:06 AM

MRO entered Mars orbit on April 6th 2006 and used primarily aerobraking until September 11th to shape it's orbit around Mars. Ain't nobody got that kind of time. In KSP, you just send up a bit more fuel.

https://solarsystem.nasa.gov/missions/mars-reconnaissance-orbiter/in-depth/

FullOfStarships t1_jca45ks wrote on March 15, 2023 at 11:36 AM

Agreed.

You could build an ion engine to do this with a tiny amount of propellant, but that would take years which completely misses the point.

Sort of like taking foot off the gas and letting a car drift to a stop.

Instead, ISS needs something like brakes. Press the pedal and the whole thing slows down. Just like modulating the brake pedal so that you stop at the lights. In this case, you apply just the right amount of brakes at just the right time to splashdown in the Southern Pacific (Point Nemo, as it's known).

Northwindlowlander t1_jc8adtp wrote on March 15, 2023 at 12:38 AM

Yeah, it really doesn't take a lot. TBH it does seem a little oversimple to me, just because the drag on the station isn't a constant- bringing it down is easy, bringing it down exactly where and when you want it to is not so simple, being able to brute force that could be very useful.

Polygnom t1_jcfky2m wrote on March 16, 2023 at 2:08 PM

The earth equatorial radius is ~6378km. The ISS is just 400km above that, or less than 6%.

99% of the energy is expended just to get into a suborbital trajectory. Its only the last couple of seconds in any spaceflight that raise the perigee from being below ground to being above the atmosphere.

In order to deorbit the station, they just need to lower the perigee enough so that drag does the rest. And a huge space station with huge solar panels has much more drag then a small, cylinder shaped capsule.