Project LR1 Skyhammer: A New Shuttle [p1]

[n0mad23]

If you haven't done so, cast your net for information on the SpaceX Raptor engine. As of last year, it had achieved 2891 kN via methane/LOX. Methane is a really good choice for reusable stages I think, as it's not so prone to coking.

 

[Donamy]

I have a parachute mesh, if you would like to lend/lease it. :hello:

 

[MaverickSawyer]

No current engine (there haven't been any methane-oxygen engines used for serious spaceflight anyway). To throw out some numbers, each of the 7 main engines will put out roughly 3 MN of thrust at around 380 s Isp using a full-flow staged combustion cycle.

Hrm... fuel-rich preburner, right? With CH4, there's no benefit to running an ox-rich preburner, as the fuel molecular weight is lighter than the oxidizer, unlike in a kerolox engine...

Also, that's going to be an impressive engine, no matter what! Can't wait to see more.

 

[fsci123]

No current engine (there haven't been any methane-oxygen engines used for serious spaceflight anyway). To throw out some numbers, each of the 7 main engines will put out roughly 3 MN of thrust at around 380 s Isp using a full-flow staged combustion cycle.

Seems like you should try sampling data from the space x raptor. They've been doing a whole lot more research on engine design than all of us.

I probably missed out on this in your original post, but what type of propulsion system will your auxiliary engine use? Hypergolic n2o4 or the usual methane system?

Also if you need a person who can help with textures or image design, feel free to pm me.

 

[orbitingpluto]

I probably missed out on this in your original post, but what type of propulsion system will your auxiliary engine use? Hypergolic n2o4 or the usual methane system?

From the OP:

Orbital maneuvering and reaction control are done with gaseous methane and oxygen rather than hypergolic fuel.

 

[fsci123]

From the OP:

Ahh... I've been made a fool of.


Wouldn't the use of meth/ox fuel throughout the vessel cause some weird problems. Like the loss of burn efficiency or needing to cool and pressurize a mega tank of low density methane...

 

[MaverickSawyer]

Not really... it's easier than LOX/LH2 for sure.

 

[kocmolyf]

Hrm... fuel-rich preburner, right?

It's a full-flow staged combustion engine, so it actually has two preburners; one fuel-rich, one oxidizer-rich. A small amount of propellant is cross-fed to each preburner.

Wouldn't the use of meth/ox fuel throughout the vessel cause some weird problems. Like the loss of burn efficiency or needing to cool and pressurize a mega tank of low density methane...

The large main propellant tanks are definitely not suitable for using with the on-orbit engines directly. The main engines use turbopumps to achieve the necessary inlet pressure, which allows the tank itself to run at low pressure. The OMS and RCS engines require higher pressures, however (hundreds to thousands of psi), so they need their own tanks.

That doesn't mean the main propellant is useless after ascent. Once on orbit, they will tend to evaporate quickly because they will be in droplet form. That's OK, though, because we have need for both CH4 and O2 gas around the vessel for pressurization and reaction control (the RCS thrusters use gas injectors). This only requires a relatively simple set of electrically-actuated piston pumps to move the gas around.

The one potential caveat is that I believe the forward RCS tanks are too far away to efficiently make use of these connections, so will probably be isolated.

 

[MaverickSawyer]

It's a full-flow staged combustion engine, so it actually has two preburners; one fuel-rich, one oxidizer-rich. A small amount of propellant is cross-fed to each preburner.

Ah. So the CH4 flows through the chamber liner to cool it down before entering the preburners. Does it flow from the tank to the pump, then to the engine, then to the burners?

 

[kocmolyf]

Ah. So the CH4 flows through the chamber liner to cool it down before entering the preburners. Does it flow from the tank to the pump, then to the engine, then to the burners?

Yep! Low pressure methane is pumped up to high pressure by the fuel turbopump. High-pressure methane cools the chamber and nozzle, dumping into the fuel preburner. It meets a small amount of O2 there and is combusted and vaporized - some of the gas goes to repressurize the propellant tank, the rest goes to spin the fuel turbine (which drives the fuel turbopump), and finally enters in the main injector to be burned in the engine.

 

[n72.75]

This looks great; anything I can do to help?

 

[kocmolyf]

I made up a new set of fins that are more plausible. The previous set had been extruded from the body so were generally warped and horrible. This time I modeled them separately and then maneuvered them into position. I also increased the staging clearance a bit. Note that the fins are still detached from the mesh and I haven't fixed the drop tank truss/plumbing after rotating the tanks slightly.

I have a parachute mesh, if you would like to lend/lease it. :hello:

I'm hoping to avoid parachute-assisted rollouts if possible, but I'll let you know.

This looks great; anything I can do to help?

Except for any feedback on the general configuration to this point, probably not a lot. However, once I get the basic model done and have it in Orbiter, I'm going to start working on a number of schematics for all the electrical systems, hydraulics, fluids/gases, and the VC layout for all of those controls. I will definitely be soliciting feedback on all of those designs since you all are the ones that are going to have to use them. :thumbup:

 

[orbitingpluto]

I've thought of few more things to ask:

1: How would a Skyhammer handle various off-pad aborts? Engines going out early in ascent, returns to launch site(RTLS) or that stuff. Let's say the Skyhammer is out over the ocean and low on energy, too low to reach land. If it can't ditch(which it probably can't), how does bailing out work?

2: Just what are the landing mass limits for Skyhammer? If it's like the Shuttles, it's probably less than it's max payload.

3: Would the Skyhammer be able to handle propellents in the payload bay, like for upper stages or delivering that propellent to a depot? There's some stuff vehicle-side(opposite to payload-side) you'll have to look into, plumbing for dumping propellent being one thing I'm certain about. Stuff about Shuttle-Centaur will probably give you ideas on what equipment/procedures might be needed, though there was a bit of politicking involved in it's cancellation; you'll have to sort out what is really a concern and what was exaggerated. This thread on NSF should help you get started in finding out more, and people involved with SSU here on Orbiter Forum should be a help as well, with DaveS being a particular person to ask.

Apologies in advance if I'm asking too much.

 

[kocmolyf]

1: How would a Skyhammer handle various off-pad aborts?

I sized the engines such that you can lose one right off the pad and still be OK (thrust-to-weight still greater than one). The lack of any solid rocket motors should open up the window of doing powered aborts significantly with respect to the Shuttle. All the internal fuel should help with this as well.

With that said, I think the fun of Orbiter is in going to space rather than not going to space, so worrying about aborts is pretty far down the list. Once I have the Skyhammer flying I would love for people to figure out how to fly it in aborts though. That would be awesome.

...how does bailing out work?

I haven't placed the crew hatches yet, but this will definitely be a consideration. In general it will probably work like the Shuttle. The caveat above applies, actually implementing any abort logic is pretty far down the list.

2: Just what are the landing mass limits for Skyhammer? If it's like the Shuttles, it's probably less than it's max payload.

Is that true? I'm not a Shuttle operations expert by any means, but I doubt they would be allowed to fly a payload they couldn't land with if they had to abort. The only exception I could think of would be the Centaur-G which they could dump the propellant from, but even then I think it was just an explosion risk (and not coincidentally it never flew). Open to being corrected on this, though.

As for Skyhammer, I would expect it to be able to land (gently) with zero fuel and max payload.

3: Would the Skyhammer be able to handle propellents in the payload bay, like for upper stages or delivering that propellent to a depot?

Absolutely! I would really like to have an integrated propellant transfer system with Skyhammer, so you can assemble things in orbit, service/fuel them, and go exploring. Hooking up propellant fill/drain lines to the payload bay is no problem. You have to worry about propellant dumping, but you probably have to dump the orbiter's internal propellant before a landing (abort or no) anyway.

 

[orbitingpluto]

I haven't placed the crew hatches yet, but this will definitely be a consideration. In general it will probably work like the Shuttle. The caveat above applies, actually implementing any abort logic is pretty far down the list.

There's some differences with the Shuttle though. Bailing out via overhead windows or hatches would probably work better for the Skyhammer than the Shuttle, since there isn't a central tail fin to collide with on the Skyhammer. Because of that tail fin, the Shuttle's preferred means of bailing out was out the side-hatch, using a extensible pole to get the astronauts out underneath the wings so as to not collide with them. Your problem isn't with wings so much as the Skyhammer's body, so I'm guessing you'd have to use something similar to the Shuttle's escape pole to get the crews clear.

In theory at least, if not in sim.:lol:

Is that true? I'm not a Shuttle operations expert by any means, but I doubt they would be allowed to fly a payload they couldn't land with if they had to abort.

Digging around online shows the limit is on payloads intended to land on the Shuttle normally; I'm not sure about aborts. I'll look into it deeper and see what comes up.

Since I've already put my foot in my mouth, it's probably a good time to admit I'm not a expert on the Space Shuttle. I do try to play the part, though I'm not on TV yet.

You have to worry about propellant dumping, but you probably have to dump the orbiter's internal propellant before a landing (abort or no) anyway.

I do know that for the Space Shuttle, propellent dumps with it's internal propellent(OMS and RCS) was done by firing the RCS thrusters, burning off propellent until mass was down to where it was wanted. For CentaurG/G-Prime, if I read it right there was dump valves located in panels on the aft end of the orbiter, one on each side of the orbiter in the area between the OMS pods and the wing.

For Skyhammer, aside from things like explosion risks, you also ought to be careful to place the propellent dumps so that they don't end up causing rotations, translations, or other propulsive stuff.

Again, in theory.

 

[MaverickSawyer]

There's some differences with the Shuttle though. Bailing out via overhead windows or hatches would probably work better for the Skyhammer than the Shuttle, since there isn't a central tail fin to collide with on the Skyhammer. Because of that tail fin, the Shuttle's preferred means of bailing out was out the side-hatch, using a extensible pole to get the astronauts out underneath the wings so as to not collide with them. Your problem isn't with wings so much as the Skyhammer's body, so I'm guessing you'd have to use something similar to the Shuttle's escape pole to get the crews clear.

In theory at least, if not in sim.:lol:

Well, if you park everyone on the top deck (assuming that there's more than one), ejection seats with MOOSE-type heat shields or B-58 Hustler style ejection seats suddenly become very possible... unlike the Shuttle. Besides, if you need to get off the Skyhammer, you'll likely need to do so in a BIG hurry, and an ejection seat is designed to do just that.
That said, they won't help on reentry, but if you need to eject then, you're pretty much toast anyways.

 

[kocmolyf]

I spent the last couple days re-working my vehicle mass solver. After tweaking and comparing I came to the conclusion that 50 tonnes to a 400 km orbit is just too much. I'm reducing that to 40 tonnes. The reduction is due primarily to a more realistic estimate of the delta-v-to-orbit and an increase in vehicle dry mass after I decided I was being too optimistic. I also added mass for unusable propellant and leftover pressurant in the tanks at burnout.

To do this mission, the main engines got a significant vacuum thrust boost to 4350 kN each. They will also be getting extendable nozzles in order to achieve good sea-level thrust for liftoff. I additionally realized I had too many RCS thrusters on the vehicle in some places, and not enough in others, so I messed around with the counts and got the thrust equaled out in each axis.

The latest internal packaging, with updated propellant loads.

On the exterior, I integrated my new fins (+ rudders and speedbrakes) into the primary mesh. I also re-did the lower and upper body flaps. I cut elevons out of the lower body flap so the Skyhammer has aero roll control now.

Current aft end.

On the short list before getting this thing into its first flight are extendable main engine nozzles, radiators in the payload bay, detailed landing gear, aero covers for the exterior drop tank plumbing, and cutting the RCS thruster nozzles out of the body. I've been holding out on the thrusters because they are a giant pain to change after the fact.

 

[Donamy]

Do you have a comparison shot ?

 

[orbitingpluto]

There's this image from page one(if your using the forum's default page settings):

And here's the latest picture of the aft end again:

It's not a proper comparison shot, but it might help.

 

[kocmolyf]

The landing gear got a big upgrade, including a reasonable deployment sequence. Still need to add mechanisms to all the doors though.