Landing a rocketship

[DDE]

Let's assume we have an honest-to-Heinlein VTVL SSTO, with a bell-like shape for optimized hypersonic aerodynamics.

How would you go about landing such a machine? Would you aerobrake engines-in, or aerobrake with your bow and then flip?

[Shpaget]

Engines front reentry doesn't seem plausible. Wouldn't they burn up?

[Frozen_Heart]

Difficult whichever way you go about it. If you take the venture star spaceplane route, you have a huge heavy heat shield on the underside and wings. Engines first means you have the complication of the engines burning up and shearing apart.

Front first seems the worst way though. Good luck not breaking up when you try to flip a massive launch vehicle in hypersonic winds.

[Bill Phil]

I'd go backwards engines in, but put them in some kind of safe area. Have a retractable heat shield on it, and it should work, assuming nothing breaks.

[tater]

Engine first. If you fire a single engine along the craft's line of flight in the atmosphere, the bow shock tends to decrease, and the craft actually speeds up due to reduced drag. If the exhaust is canted outwards slightly, you create a  set of offset bow shocks that overlap (if 3 engines, you could imagine the 3 parachutes, but in reverse, and closer to the craft). This is a drag-multiplier and actually can slow the craft more due to drag than it loses to propulsive braking. 

In another thread someplace I posted a video of a PhD defense about supersonic retropropulsion, and this was basically what he discussed, it was worth a watch.

Note that the Dragon 2 engines are canted in this way, which is not an accident. It's a reason NASA is so interested in Red Dragon as a testbed.

Edited August 13, 2016 by tater

[Wjolcz]

An inflatable/retractable heat shield between the engines makes most sense to me. Not sure how to deal with a single-engine design though. Ballutes perhaps?

Edited August 13, 2016 by Veeltch

[kerbiloid]

Which end should be up: big or little?. Little-Endians vs Big-Endians competition.

In KSP, for my private "grim citadel of mad evil scientist" setting, I plan to use VTVL basically looking like this:

Spoiler

But modified:
1) Only side engines, on the pylons.
2) Pylons are retractable.
3) Narrow top and wide bottom. Bottom is wider than on the picture, Bottom is covered with heatshield, no engines there. But not too wide, otherwise the rocket couldn't pitch,
4) When pylons are retracted, their engines are protected by the bottom heatshield.
5) When pylons are expanded, these cigar-looking things are nacelles with fixed main engines, gimballed vernier+landing engines and RCS engines. Also the pylons with cigars are radiators, landing legs and fins,
6) Starts with expanded pylons and all engines on. After deorbiting retracts pylons and then aero(brakes? breaks? - by luck), with big-end down. When speed is subsonic (if the ship still exists), expands the pylons back and lands with vernier engines.
7) VTVLing is facultative. The upper part of the rocket is its exact copy scaled down. It can be a spaceship or a cargo. It can decouple (then the rocket is only a reusable launch vehicle) or not (then the rocket is VTVL).
8) All parts land on a top of a wide and low tower aside the castle. If possible - there is a cargo elevator platform which descends them for refurbishment, if not possible - I'll press "recover vessel" and imagine as the elevator were there.

When using a (more or less) portable thermonuclear reactor (B+H, aneutronic) and plasmatic nozzles, probably from KSPI-E mod, things totally change.
There is an enormously huge budget of delta-V, you can lift and descend slowly.
But the ship is huge and load/unload operations are hard if it's vertical.
So, a thermonuclear VTVL freighter would have horizontal, helicopter-style, fuselage; main engines facing back and ascent engines facing down.As a result it would look like the ship from excellent V8Jester's animation.
 

4 minutes ago, Veeltch said:

An inflatable/retractable heat shield between the engines makes most sense to me.

NASA ADEPT

Also on Kerbin

[DDE]

3 hours ago, tater said:

Engine first. If you fire a single engine along the craft's line of flight in the atmosphere, the bow shock tends to decrease, and the craft actually speeds up due to reduced drag. If the exhaust is canted outwards slightly, you create a  set of offset bow shocks that overlap (if 3 engines, you could imagine the 3 parachutes, but in reverse, and closer to the craft). This is a drag-multiplier and actually can slow the craft more due to drag than it loses to propulsive braking. 

In another thread someplace I posted a video of a PhD defense about supersonic retropropulsion, and this was basically what he discussed, it was worth a watch.

I wonder how much gimbal is needed to achieve the same effect.

4 hours ago, Shpaget said:

Engines front reentry doesn't seem plausible. Wouldn't they burn up?

I think it really depends on what those engines are. Anything SSTO-capable might be adapted to stupidly high heat fluxes anyway.

I used to make my orbit-capable Falcon 9R rip-off reenter engine-first. And yeah, @Veeltch, it involved a trailing Kermageddon ballute. And even then it was a very tight balancing act.

[tater]

Very little gimble, a few degrees.

[tater]

(guess it was thesis, not dissertation)

[Firemetal]

Engine first and do a retro burn before re-entry like F9. But as said above,

5 hours ago, Frozen_Heart said:

Difficult whichever way you go about it. If you take the venture star spaceplane route, you have a huge heavy heat shield on the underside and wings. Engines first means you have the complication of the engines burning up and shearing apart.

Front first seems the worst way though. Good luck not breaking up when you try to flip a massive launch vehicle in hypersonic winds.

a spaceplane  re-enters nose in front so it doesn't have to flip over to land in hypersonic wind.

[Frozen_Heart]

20 minutes ago, Firemetal said:

Engine first and do a retro burn before re-entry like F9. But as said above,

a spaceplane  re-enters nose in front so it doesn't have to flip over to land in hypersonic wind.

Yeah but it is sometimes suggested to enter nose first to protect the engines and then flip round and land like a falcon 9. (I don't think this is a great idea)

[Firemetal]

Just now, Frozen_Heart said:

Yeah but it is sometimes suggested to enter nose first to protect the engines and then flip round and land like a falcon 9. (I don't think this is a great idea)

Nope. It's much simpler to re-enter and land engine first.

[Frozen_Heart]

3 minutes ago, Firemetal said:

Nope. It's much simpler to re-enter and land engine first.

Only question with that is can the engine bells withstand re-entry?

[Firemetal]

Just now, Frozen_Heart said:

Only question with that is can the engine bells withstand re-entry?

As I said previously, it would do an entry burn like F9

[Frozen_Heart]

6 minutes ago, Firemetal said:

As I said previously, it would do an entry burn like F9

If you want to reduce orbital velocity to close to that of the Falcon 9 entry, you'll need the dV to not only SSTO to earth orbit, but then almost completely reverse it back to a few km/s. That is well above what chemical engines can do.

[Firemetal]

Just now, Frozen_Heart said:

If you want to reduce orbital velocity to close to that of the Falcon 9 entry, you'll need the dV to not only SSTO to earth orbit, but then almost completely reverse it back to a few km/s. That is well above what chemical engines can do.

I know that. If it doesn't have the DV, then use a deployable/retractable heat shield to re-enter like the one in KSP only it can retract so that the SSTO can land. I'd also add a couple of drogue chutes to slow it down even more and make the landing easier.

[StrandedonEarth]

3 hours ago, Frozen_Heart said:

If you want to reduce orbital velocity to close to that of the Falcon 9 entry, you'll need the dV to not only SSTO to earth orbit, but then almost completely reverse it back to a few km/s. That is well above what chemical engines can do.

Well, if you get the engine(s) lit before the entry wind makes that impossible, then the plume could protect the engine(s) through the worst of the re-entry conditions, until it slows down to Falcon-esque speeds. Not firing the engine for braking so much as for protection, keeping the bow shock off the engine bells.

Edited August 14, 2016 by StrandedonEarth
typo again

[Bill Phil]

41 minutes ago, StrandedonEarth said:

Well, if you get the engine(s) lit before the entry wind makes that impossible, then the plume could protect the engine(s) through the worst of the re-entry conditions, until it slows down to Falcon-esque speeds. Not firing the engine for braking so much as for protection, keeping the bow chock off the engine bells.

Thing is, the compression shock will compress the exhaust as well. Could still work though

[kerbiloid]

2 hours ago, StrandedonEarth said:

the plume could protect the engine(s)

Engine's ISP is 3000 m/s, air speed is ~7000 m/s...

[DDE]

@Bill Phil@StrandedonEarth@Frozen_Heart, what if we try to factor in a magnetic reentry shield?

Edited August 14, 2016 by DDE

[magnemoe]

6 hours ago, kerbiloid said:

Engine's ISP is 3000 m/s, air speed is ~7000 m/s...

It will still protect engine as it pushes the shock front away from the ship, this has been seen on Falcon 9 braking burns. 

[Tex_NL]

One does not need to re-enter either nose or tail first. A belly first shuttle style re-entry with a tail landing is still very much within the realm of possibilities.
Re-enter just like the shuttle and glide towards the landing area. Pull the nose up to vertical until it stalls to bleed off horizontal speed. Open nose mounted airbrakes and/or grid fins to come in for a controlled tail landing.

Edited August 14, 2016 by Tex_NL

[Nibb31]

The Dragon V2 shape looks like a sound design, although we can't say it's been proven yet. The engines are side mounted and protected from the air-flow. There are co-sine losses though, which are going to eat into your dV. The whole idea of carrying enough dV to SSTO is implausible anyway.

I think a nice evolution would be something that would combine the Falcon 9 upper stage with a Dragon-like design. The first stage would reenter on its own, and this "Super Dragon" would be big enough to carry enough dV to achieve orbit and reenter. Some people are speculating that this is how the MCT will work.

Edited August 14, 2016 by Nibb31

[shynung]

5 hours ago, DDE said:

what if we try to factor in a magnetic reentry shield?

MSNW LLC was recently putting forward that idea.

Quote

In the NASA Phase I Phase I a full system was designed for Neptune and Mars missions. This analysis showed that a 200 kg, 2 m magnet could generate a 9 m radius Magnetoshell for Neptune aerocapture with a 21 km/s injection at a peak force of 150 N entirely removing the need for a TPS. At Mars, a 2.5 m magnet could generate a 21 meter radius Magnetoshell, providing aerocapture for a 60 metric ton payload removing the dedicated aerocapture TPS and saving $2 B for DRA 5.0. Finally, a stationary 1.6 meter argon Magnetoshell was fully demonstrated and a 1000:1 increase in aerodynamic drag was found. In addition, by decrease the dynamic pressure requirements while simultaneously shielding the spacecraft, heating during an Aerocapture maneuver could be reduced by 10,000X.

http://msnwllc.com/space-technology

Not shillin' or anything, just recently dug it out.

Edited August 14, 2016 by shynung