SSTO Pure Liquid Fuel Space Plane

[ayak]

I have spent some time designing a pure liquid fuel space plane and this is what I have come up with:

http://lookpic.com/O/t2/1055/UeznrsZ.jpeg' alt='UeznrsZ.jpeg'>

The problem that I am having is that once it is in orbit at around 100k there is only 1000m/s delta v left and I am trying to use this for interplanetary travel. Not sure what the solution is.

Edited July 7, 2015 by ayak

[Red Iron Crown]

Welcome aboard!

Are you sure you are totally against oxidizer at all? An interplanetary SSTO plane becomes much easier using Rapiers in closed cycle mode to help kick periapsis far enough ahead for your nukes to do their job. I would also consider going with a single nuclear engine rather than two, they are quite heavy and eat into delta-V.

[Edax]

I have spent some time designing a pure liquid fuel space plane and this is what I have come up with:

The problem that I am having is that once it is in orbit at around 100k there is only 1000m/s delta v left and I am trying to use this for interplanetary travel. Not sure what the solution is.

[i can't see your image]

You need to build a LF refueling station in orbit of Kerbin using either MK1 or MK3 LF parts. Dock with it, and gas up. SSTO's cannot effectively travel after they burn their fuel escaping Kerbin unless they get some gas whilst in orbit.

[Red Iron Crown]

SSTO's cannot effectively travel after they burn their fuel escaping Kerbin unless they get some gas whilst in orbit.

Cannot? *Cough*

[Edax]

Cannot? *Cough*

Yes, they cannot "effectively" travel. I didn't say they couldn't do it. You want to leave Kerbin orbit with a full tank so you can go anywhere and come back. A lot of the spaceplane is dead weight in space, so you need to top off the tanks to compensate.

[Sharpy]

Yep, you just started something big.

LKO fuel station. A Minmus mining operation. A fuel carrier to deliver the fuel from Minmus. A fleet of trucks to bring the fuel from Minmus surface to the carrier. Easily a week of gameplay. Have fun!

[Red Iron Crown]

Yes, they cannot "effectively" travel. I didn't say they couldn't do it. You want to leave Kerbin orbit with a full tank so you can go anywhere and come back. A lot of the spaceplane is dead weight in space, so you need to top off the tanks to compensate.

How are you defining "effective" here? Much of the plane will be dead weight in space whether one refuels or not.

[Edax]

How are you defining "effective" here? Much of the plane will be dead weight in space whether one refuels or not.

Spaceships can get away with very light designs and can ditch mass with staging, while spaceplanes have to drag around it's wings, plus, SSTO spaceplanes have trouble removing dry mass from itself, so it's less fuel efficient traveling in space, that's one of the drawbacks to spaceplanes. To compensate for the extra dry mass, you add fuel sometime during the journey.

[ayak]

I don't have the rapiers or ISRU unlocked yet and I just wanted to see if I could build a pure liquid fuel plane that can be useful after it got to orbit.

The reason that I am using two nukes is there is not enough thrust to keep the plane climbing once the air breathing engines burn out. Would adding a second set of radial intakes keep them going longer in the upper atmosphere because then I could dump the extra nuke?

Right now I am just sending up unmanned refuel missions until I have the ISRU unlocked and set up.

[Red Iron Crown]

Extra intakes have little effect, if you are using the LV-Ns to finish raising Ap then you might need both of them.

[ayak]

That is what I was thinking. The only problem now is the nose does not want to stay up. Is there a mod that lets you know if the plane has enough lift at certain speeds and altitudes?

[ajburges]

LF only space planes are hard.

For 4 km/s dV on nukes with a starting TWR of .7 (the highest TWR where nukes are typically mass optimal) you need 3.5 t (700 units) fuel per engine (and â…› tank mass) for a budget of 1.8 t payload per engine for a total mass of 8.7 t. The orbit mass of a Whiplash (engine, intake, tank, and round up for landing fuel) is 3 t. If you overload 2 nukes to a jet, that leaves .3 t a nuke for payload and wings! You want 3-4 t for crew cabin and support. (docking, panels, reaction wheel, monoprop, etc) You need to compromise on TWR (complicating accent profile) or dV (limiting range) for better payload fractions.

In 1.02 you could fly with good lift and low drag at 32 km until you gained orbital speeds. That allowed a more predictable if not more efficient accent for nuclear planes. Unfortunately, this doesn't seem to work anymore for 1.04 (the AoA needed for level flight killed horizontal velocity). Instead, insertion burn must be done on ballistic trajectory. 1300 m/s (1600 vacuum) is a lot of acceleration to get out of those nukes on a suborbital trajectory.

Since there are almost no LF only structural parts and RAPIERs have a higher flight envelope, I recommend using RAPIERs for nuclear space planes and using the LOX your structural parts can hold regardless as a booster after airbreathing mode starves completely.

IMHO, if you don't have RAPIERs, the only association nukes should have with your planes is as a payload. The numbers just don't work out well.

Edited July 7, 2015 by ajburges

[Sharpy]

Well, yesterday I did bring a tiny SSTO to the orbit through atmospheric flight with a very slow climb. It took an unreasonably long time but it worked. Two whiplashes, one Nuke, three LF fuselages (the ones for whiplashes drained to 1/4 capacity), smallish wings and a probe core instead of a pilot. It's mostly useless because it can't take any payload, but it works. It was a very, very long climb as I was gaining maybe 1-2m/s per second, and only climbing as lift gained through the extra speed (and extra centrifugal force) allowed.

You can expect maybe 400m/s dV from the nukes in the ballistic flight. There's no way in hell you could get 1200dV out of them before sinking back into the atmosphere if you start at 1200 you can get from the whiplashes.

For that I had a different approach: an intermediate engine. I built a very heavy MK3 SSTO with a Rhino for bringing it into orbit from the 25km where Whiplashes die. Again, very impractical but again it works.

Edited July 7, 2015 by Sharpy

[Pyromancer]

This is what I use to give tours, good enough for Mun flybys without refueling but not for much else

http://i.imgur.com/Ct9rhhH.jpg

[Edax]

LF only space planes are hard.

For 4 km/s dV on nukes with a starting TWR of .7 (the highest TWR where nukes are typically mass optimal) you need 3.5 t (700 units) fuel per engine (and â…› tank mass) for a budget of 1.8 t payload per engine for a total mass of 8.7 t. The orbit mass of a Whiplash (engine, intake, tank, and round up for landing fuel) is 3 t. If you overload 2 nukes to a jet, that leaves .3 t a nuke for payload and wings! You want 3-4 t for crew cabin and support. (docking, panels, reaction wheel, monoprop, etc) You need to compromise on TWR (complicating accent profile) or dV (limiting range) for better payload fractions.

In 1.02 you could fly with good lift and low drag at 32 km until you gained orbital speeds. That allowed a more predictable if not more efficient accent for nuclear planes. Unfortunately, this doesn't seem to work anymore for 1.04 (the AoA needed for level flight killed horizontal velocity). Instead, insertion burn must be done on ballistic trajectory. 1300 m/s (1600 vacuum) is a lot of acceleration to get out of those nukes on a suborbital trajectory.

Since there are almost no LF only structural parts and RAPIERs have a higher flight envelope, I recommend using RAPIERs for nuclear space planes and using the LOX your structural parts can hold regardless as a booster after airbreathing mode starves completely.

IMHO, if you don't have RAPIERs, the only association nukes should have with your planes is as a payload. The numbers just don't work out well.

LF spaceplanes are easy, just bolt them onto a non-LF only SSTO. Then the LV-N only has to operate once in orbit.

[ygarl]

Could always strap a pair of decent boosters to the topside - making sure they are centered nicely above the CoM, set them on low thrust (50ish%), run very low throttle on the main engines until the boosters run out.

I've had good luck with that (just making sure they don't eject onto your avionics/control surfaces!)

[GoSlash27]

My first stab at an all-fuel spaceplane was successful in 1.04. I struggled with these in 1.02.

Here's what I did:

It makes orbit with half it's fuel still unused, so there's lots of room for payload ratio if you scale it.

Best,

-Slashy

Edited July 8, 2015 by GoSlash27

[Sharpy]

By the way, do you have cubic octagonal struts unlocked yet?

This is an absolute bare minimum SSTO proof-of-concept.

It's capable of making it to the orbit and back and about nothing else, but if you add more fuel tanks this becomes a viable option.

Attach a cubic octagonal strut to the middle of a liquid fuel fuselage - where the node is, but not to the node - don't hold 'alt'. Rotate it so that it's sunken in.

Attach the nuke to it in such a way that most of it is sunken inside the fuselage.

Attach a whiplash over the nuke (to the fuselage, not to the nuke).

Strap an intake on the front.

Now you have a jet+nuclear booster with enough own fuel to lift itself to the orbit, in a neat package that's less than two fuselages size. Treat this as a single "one engine" subassembly and try building your SSTOs with these, Extra fuel means extra payloads or extra dV. An extra ton of fuel can get an extra two tons of payload/structure/fuel/whatever into orbit.

Ascent profile: slow atmospheric climb. Don't try fish jumps above the atmosphere.