Smallest krewed orbiter

[Jebediah Kerman Jr.]

Bradley Whistance recently made a 1.4 ton SSTO:

https://www.youtube.com/watch?v=6vGBuhzkukU

SSTOs generally need to be larger/heavier than staged rockets, so how small can you guys build a "krewed" staged rocket?

I await your submissions!

Edited February 19, 2019 by Jebediah Kerman Jr.

[catonthekbd]

That is a two stage rocket. The jet enginer got "staged" by being destroyed by the rocket engine

/pedant mode = off

 

[Jebediah Kerman Jr.]

Okay, maybe it did get "staged"

I just wanted to see if anyone could build something even smaller.

[jinnantonix]

What engine(s) were used in the Bradley Whistance "SSTO"?  Are they stock?

[Jebediah Kerman Jr.]

34 minutes ago, jinnantonix said:

What engine(s) were used in the Bradley Whistance "SSTO"?  Are they stock?

Yep, they are stock. I believe Juno and Spark.

12 hours ago, catonthekbd said:

That is a two stage rocket. The jet enginer got "staged" by being destroyed by the rocket engine

Wait, I watched the video again. The engine appears to be burnt off, but that was just it flaming out (Brad uses Realplume). You can still see it in the staging. In any case, this thread is about building the smallest possible staged krewed rocket, not an SSTO. 

[jinnantonix]

12 hours ago, Jebediah Kerman Jr. said:

The engine appears to be burnt off, but that was just it flaming out

I agree.  The craft seems to have clipped the Juno and Spark together making a "Jark" or "Spuno"  I assume action keys are used to activate and shutdown each engine at various times during ascent.  The Spark is required at launch to get to speed for oxygen intake, the Juno is used to get from sea level to high altitude, then the Spark does the orbital injection and de-orbit.  

Your question is:  can a more efficient craft be made by staging the Juno for ejection when it cuts out at high altitude?  The problem I see is that this would throw out the craft balance massively and so make gliding to the surface problematic.  The Juno would also need to be mounted behind the fairing base, so the whole craft would need to be rethought.

 

[Jebediah Kerman Jr.]

My idea is that the design would be less than 1 ton, and be a conventional rocket rather than a glider. Maybe a juno bottom stage, a spark middle stage, and maybe an ant for upper stage. Given that a 1.3 ton rocket can get to Minmus, a krewed sub-1 ton craft should  be able to get to orbit.

 

[KingDominoIII]

33 minutes ago, Jebediah Kerman Jr. said:

My idea is that the design would be less than 1 ton, and be a conventional rocket rather than a glider. Maybe a juno bottom stage, a spark middle stage, and maybe an ant for upper stage. Given that a 1.3 ton rocket can get to Minmus, a krewed sub-1 ton craft should  be able to get to orbit.

 

BW made an SSTO somewhere around the realm of .5 tonnes a while ago. It was unmanned and used a single spark engine. I don't think a sub-1 tonne craft is possible considering how much the upper stage of his Minmus craft weighed.

Edited February 21, 2019 by KingDominoIII

[Jebediah Kerman Jr.]

11 hours ago, KingDominoIII said:

BW made an SSTO somewhere around the realm of .5 tonnes a while ago. It was unmanned and used a single spark engine. I don't think a sub-1 tonne craft is possible considering how much the upper stage of his Minmus craft weighed.

Brad also thought that a Single Stage to Tylo and back was impossible without ISRU. He later proved himself wrong.

[KingDominoIII]

9 hours ago, Jebediah Kerman Jr. said:

Brad also thought that a Single Stage to Tylo and back was impossible without ISRU. He later proved himself wrong.

The craft was literally 6 parts. Spark, two Oscar-Bs, OCTO 2, small nosecone, and basic fin. The OCTO is the lightest probe core, the fin is the lightest fin, the nosecone could maybe go but I think that it's lighter than the fuel you'd need to compensate. The spark is the only engine that can effectively work both in and out of atmosphere. Fuel margins were nonexistent. 

[Jebediah Kerman Jr.]

Hmm. Which craft are you talking about?

[KingDominoIII]

18 hours ago, Jebediah Kerman Jr. said:

 

 

[Jebediah Kerman Jr.]

Oh, but that's neither krewed nor staged. I'm talking about a staged rocket with a Kerbal in it.

[KingDominoIII]

27 minutes ago, Jebediah Kerman Jr. said:

Oh, but that's neither krewed nor staged. I'm talking about a staged rocket with a Kerbal in it.

Yes. The kerbal and staging mechanism only add weight. By the time you've added them, it's over a ton.

[Jebediah Kerman Jr.]

Hmm. Even if the final product would be more than a ton, it would definitely be less than 1.3 tons (to Minmus).

In theory, the final orbiter would not need fuel, it would just be a passive heatshield (radiator) and a seat, because the EVA pack could be used to push it from a suborbital path to stable low orbit and back again. So you would only need the first (and/or second) stage(s) to push the craft onto a suborbital trajectory, then circularize using the jetpack.

[KingDominoIII]

11 hours ago, Jebediah Kerman Jr. said:

Hmm. Even if the final product would be more than a ton, it would definitely be less than 1.3 tons (to Minmus).

In theory, the final orbiter would not need fuel, it would just be a passive heatshield (radiator) and a seat, because the EVA pack could be used to push it from a suborbital path to stable low orbit and back again. So you would only need the first (and/or second) stage(s) to push the craft onto a suborbital trajectory, then circularize using the jetpack.

The thing is, you can't place a seat on a heat shield. In addition, the jetpack can't be used while seated, which decreases its efficiency unless you design around using it and have the wiggle room for structural parts. If we look at Brad's Minmus mission, his final stage is really minimal: a small radiator, Oscar-B tank, seat, and a spider engine. I did the math, and he had .09 tonnes left of fuel when he reached orbit. That's not the kind of savings we were talking about. The obvious solution is to eliminate the stage altogether but that, paradoxically, adds weight because of the juno and fairing weight.

EDIT: I read through his comment section in case he mentioned this question- and he does, verbatim! He says that the vehicle can maybe be reduced to 1.2 tonnes for orbit, assuming there isn't a more efficient, different approach. This matches my own findings.

Edited February 23, 2019 by KingDominoIII

[Jebediah Kerman Jr.]

What I was thinking was that the Kerbal would get out of the seat and push. Maybe the seat and heatshield would be attached to an octagonal strut?

[KingDominoIII]

16 hours ago, Jebediah Kerman Jr. said:

What I was thinking was that the Kerbal would get out of the seat and push. Maybe the seat and heatshield would be attached to an octagonal strut?

Okay, let's assume perfection because I have no way of estimating the losses from off-center thrust with the Kerbal. Let's also not account for the deorbit burn, as it's minimal. Kerbals have 600 m/s of dV. Brad's final stage expends 900 dV to circularize. That leaves us with a final stage requiring only 300 dV. 

That's the equation for delta v. m sub 0 is wet mass and m sub f is dry mass. v sub e is exhaust velocity, equal to g*Isp.

Let's assume the spider engine is in vacuum when operating. This gives us an Isp of 290. Dry mass ads up to .21 tonnes. 

300=(290*9.8)*(ln(x/.21))

Wet mass is .23 tonnes. Let's calculate his current wet mass.

.4 tonnes.

So you drop .17 tonnes maximum with this approach, not accounting for losses to maneuvering. I also didn't account for the weight of the craft, but I'm sure that it would hinder the kerbal significantly. Unfortunately you can't really calculate it as kerbals don't lose mass when they use their thrusters and don't have Isp. Another thing I didn't think about was the possibility of using the dumpling tank, which is lighter than the Oscar-B. I don't think that it's really significant enough to account for though, as it's only .02 tonnes lighter dry than the Oscar-B.

Edited February 24, 2019 by KingDominoIII

[Jebediah Kerman Jr.]

Ah. It seems you have invoked the wrath of Tsiolkovsky.

(When I do Δv, I just "wing it," making guesstimates that usually end up with at least a kilometer per second more or less than I need)

I concede defeat. Happy Delta-Veeing!  

[KingDominoIII]

2 hours ago, Jebediah Kerman Jr. said:

Ah. It seems you have invoked the wrath of Tsiolkovsky.

(When I do Δv, I just "wing it," making guesstimates that usually end up with at least a kilometer per second more or less than I need)

I concede defeat. Happy Delta-Veeing!  

Assuming you don't require return, you might be able to get more significant savings, which should be discussed.

[Jebediah Kerman Jr.]

Return is implied, who wants to be stuck in orbit for all eternity?

[sevenperforce]

Well not very well implied.

So to be clear, this challenge is:

• Send a Kerbal into orbit
• And bring him back to the ground alive
• Using staging in your vehicle at some point
• For the lowest possible takeoff mass, including the Kerbal.

Right?

[Jebediah Kerman Jr.]

Yep.

[sevenperforce]

Let's see...I've gotten it just under 3 tonnes to date. Lemme see how much further I can trim it.

[Jebediah Kerman Jr.]

OK, good luck.