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Post by Enderminion on Apr 6, 2017 16:25:54 GMT
nope not me either
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Post by The Astronomer on Apr 6, 2017 16:30:35 GMT
I can mod if I have data.
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Post by RiftandRend on Apr 6, 2017 16:47:59 GMT
For water NTRs you should make the engine throat very wide. You can get up to 4.3 km/s with the extra dissociation fraction.
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Post by sevenperforce on Apr 6, 2017 17:32:55 GMT
For water NTRs you should make the engine throat very wide. You can get up to 4.3 km/s with the extra dissociation fraction. Oh, nice. The OP in the other forum wanted a dropship that could enter from orbit, land vertically, ISRU to refill its proptanks over a period of a few days, and then return to orbit in a single stage. Leaving consideration of the dropship configuration aside, the engine I was thinking of was a nuclear pebble-bed water turboramrocket. For the ship's power, run a steam turbine geared to the intake fan; the steam opens to a condenser at low-power operation but is vented into the exhaust portion of the bypass shroud during engine operation. The same vents can also be flooded with water to rapidly cool the engine bell after shutdown or to multiply takeoff thrust at the expense of specific impulse. When landing on mostly-empty tanks, the intake fan and open-cycle cooling exhaust alone will be sufficient to pull a gee or so, enabling a vertical landing without melting the landing site. Takeoff, on the other hand, would definitely melt the landing site.
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gorthaff
New Member
I can't for the life of me come up with anything smart or witty. <-THIS-> is all you get.
Posts: 17
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Post by gorthaff on Apr 6, 2017 20:18:38 GMT
If KSP is any accurate, an SSTO would coast for a long time in the upper atmosphear picking up spead, and only using its vacuum optimised drive to break into an actual low orbit. TWR seems to be important, so the jets dont waste fuel accelerating the NTR and its fuel. Of course if you dont want to have to refuel in orbit to continue operations, it might be wiser to optimize for high Dv instead.
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Post by newageofpower on Apr 6, 2017 20:50:17 GMT
SSTOs want to maximize Thrust and TWR while retaining useful dV. Since atmospheric effects obviate Boron (chemically reacts with Oxygen), some sort of Amorphous Carbon design is indicated. Regenerative cooling will allow us to reinforce its mediocre structural properties with composite construction.
Assuming heat flow and core temperature limited by Uranium Oxide, we may want to look at heavy hydrocarbons, probably RP-1 due to experience in handling this propellant in current chemical rocket programs.
With RP1, vacuum exhaust velocities in excess of 5.2 km/s can be obtained with a rocket engine maintaining TWRs in the thousands, but due to safety margin concerns the engine may be designed with a TWR merely in the hundreds - a far greater issue is fuel tank design.
Minmaxed CoADE paper thin fuel tanks with ludicrous mass ratios are unlikely to retain structural integrity under high acceleration and gravity; but mass ratios in the low hundreds using advanced composite construction techniques are quite plausible. Overall structural framing needs will further increase dry mass, however, bringing us within an order of magnitude of current chemical rocketry in payload efficiency.
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Post by gedzilla on Apr 6, 2017 20:55:07 GMT
I still think they should just use Decane or Methane
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Post by sevenperforce on Apr 6, 2017 20:59:51 GMT
If KSP is any accurate, an SSTO would coast for a long time in the upper atmosphear picking up spead, and only using its vacuum optimised drive to break into an actual low orbit. TWR seems to be important, so the jets dont waste fuel accelerating the NTR and its fuel. Of course if you dont want to have to refuel in orbit to continue operations, it might be wiser to optimize for high Dv instead. That's precisely how airbreathing SSTOs are flown, particularly with the RAPIER engine (the in-game counterpart of the SABRE). Of course, not all SSTOs are airbreathers, and even an airbreathing SSTO can still do VTVL. Airbreathing is better with an NTR than with a chemical engine, because you can operate in the scramjet velocity range without the pesky requirement of maintaining combustion stability.
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gorthaff
New Member
I can't for the life of me come up with anything smart or witty. <-THIS-> is all you get.
Posts: 17
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Post by gorthaff on Apr 6, 2017 21:05:09 GMT
Is there enough air around at those heights to serve as propellant? Or am I misunderstanding what you are telling?
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Post by sevenperforce on Apr 6, 2017 21:25:14 GMT
I still think they should just use Decane or Methane With a vacuum specific impulse of 530 seconds and a thrust to weight ratio of anything over 100, you only need a tank mass ratio of 25 or so to make reusable, payload-positive SSTO trivial. But since RP-1, decane, and methane are likely outside the range of rapid ISRU, that's not terribly useful for the OP on the other forum. What was the listed specific impulse of decane?
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Post by Enderminion on Apr 6, 2017 21:50:00 GMT
I have an SSTO missile, 10.6km/s Dv is enough to make it to low earth orbit, in fact Dv needs to be at least 9.4km to make LEO. it used to use Boron injectors on the motors but litium is lighter and still worked with no other changes then improved TWR
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Post by sevenperforce on Apr 6, 2017 22:12:09 GMT
Is there enough air around at those heights to serve as propellant? Or am I misunderstanding what you are telling? Kerbal's Karman line is at 70 km rather than 100 km but it follows a pretty standard density/pressure curve, so there are ascent profiles for airbreathing SSTOs like this: s11.postimg.org/4ufwnask3/profile.png
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Post by gedzilla on Apr 6, 2017 22:15:40 GMT
I still think they should just use Decane or Methane With a vacuum specific impulse of 530 seconds and a thrust to weight ratio of anything over 100, you only need a tank mass ratio of 25 or so to make reusable, payload-positive SSTO trivial. But since RP-1, decane, and methane are likely outside the range of rapid ISRU, that's not terribly useful for the OP on the other forum. What was the listed specific impulse of decane? I can get an exit v of roughly 5.4km/s from Decane
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Post by gedzilla on Apr 6, 2017 22:16:49 GMT
Whats a rapid ISRU ?
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Post by Durandal on Apr 6, 2017 22:23:14 GMT
In-Situ Resource Utilization. Shoveling ice rocks into your fuel tank to make the rocket go.
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