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Jestersage

Enough Delta V for a station?

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I am trying to create a SSTO taxi without going overboard on the engines in order to maintain a smooth outline. However, while it can go into LKO, I am wondering if 700 ish Delta V is sufficent for a transfer to a LKO station. I am debating whether to put the station in 150k or 250k.

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10 minutes ago, Jestersage said:

I am trying to create a SSTO taxi without going overboard on the engines in order to maintain a smooth outline. However, while it can go into LKO, I am wondering if 700 ish Delta V is sufficent for a transfer to a LKO station. I am debating whether to put the station in 150k or 250k.

Tl;dr: yes, easily.

The dV you need depends on how "high" your station is. So if you place your station in a higher orbit, you need more dV to reach it. However, 700 m/s dV should still be sufficient to reach your station if it is at an altitude of 250 km, and to deorbit again. Generally, you need about 100-150 m/s dV for deorbiting. 

Edit: in fact, you need 248 m/s dV to reach a 250 km orbit from a 75 km parking orbit. Source: https://instacalc.com/50998

So to me it seems, you have sufficient dV to reach a station in an orbit with an altitude of 250 km.

 

Also, the disadvantage of having a station in a lower orbit is that you have to wait longer for a hohmann transfer to occur, as the difference in orbital periods between the orbits is smaller. So it can happen that you have to wait 10 orbits before you can transfer to the station, which would not be the case if your station is in a higher orbit.

Edited by DaMaster_Architect
added calculation

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@Jestersage:

If you leave 250 m/s for a de-orbiting reserve (giving you 450 m/s to play in orbit), you can go up to about 450 km on the 700 m/s you have when you reach orbit.  You actually only need 225 m/s to de-orbit, so that leaves you a tiny 25 m/s emergency reserve for fine matching, docking, fixing pilot errors, flying the SSTO in atmosphere to a controlled landing, and other fun.  I made some assumptions here:  namely, that you would de-orbit to a re-entry periapsis of 59 km, that you would go for direct re-entry rather than circularising at 75 km first, and that you had no other fuel held in reserve for other manoeuvres, landing, &c.

If you decide to put your station at 250 km, @DaMaster_Architect's maths are good; you'll need 133 m/s to de-orbit from there, though.  Don't leave yourself short of fuel.

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I like putting a station at ~165-170km. It’s just above the line at 160km where the game unloads the high-res Kerbin terrain textures, and uses lighter low-res textures. So anything above that line will generally run physics a little faster, which is important as your stations grow. Still plenty high that a rendezvous from an arbitrary 75-80km orbit doesn’t take long. 

I don’t see any real disadvantage to a higher orbit like 250km, just requires a bit more delta-V. I like to use SSTOs with pretty narrow margins, so I like as low as practical for my transfer station. 

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