Flight Question Soyuz TMA (Thorton) Fuel Question

[TG626]

How much is needed to undock and deorbit from the ISS?

(I've looked here and on the net and I haven't found it - the closest I've seen is that in real life, Soyuz does a 4 minute burn to de-orbit. <- seems a bit long for the 70k Periapsis called for in the "Soyuz TMA Manual" manual for reentry.)

Orbiter 2010 P1
Soyuz TMA Ver 1.3 by Thorton

 

[N_Molson]

Keep 250-300 kgs and you'll be safe. In real life, I think they deorbit the BO with the spacecraft, and jettison it just before reentry, hence a longer burn time (but I may be wrong).

Also, I don't know which thrust mode is used in real life. The 6.1 kN seems logical, but if they use the 700 N for some reason, it takes more time.

 

[Urwumpe]

Keep 250-300 kgs and you'll be safe. In real life, I think they deorbit the BO with the spacecraft, and jettison it just before reentry, hence a longer burn time (but I may be wrong).

No, you are right. Jettisoning the BO before deorbit caused some problems when the deorbit burn failed - a day in a really tiny capsule without toilet or better food than survival packs.

 

[garyw]

Wouldn't the dV required for the burn vary from mission to mission dependant on mass of the spacecraft?

 

[N_Molson]

No, you are right. Jettisoning the BO before deorbit caused some problems when the deorbit burn failed - a day in a really tiny capsule without toilet or better food than survival packs.

I can understand that. They have a SA at the local space museum and I sat into it... There is a dummy inside, and with another person, you just can't move a finger without hitting anything... It's really small and spending more than a few hours inside with 2 other people is probably not fun

And BTW, I'm only 172 centimeters tall, and rather a "small frame" by todays standard, someone who is 200 centimeters high just can't sit correctly.

 

[Grover]

Wouldn't the dV required for the burn vary from mission to mission dependant on mass of the spacecraft?

the dV wouldnt, since velocity and mass are not linked, but fuel would.

though in this case, its already accounted for, hence the large variation in fuel masses quoted before.

and due to the low fuel:dry mass ratio of a fully laden Soyuz, it doesnt make much difference anyway