Hypothetical SpaceX SSTO

[bioelectromechanic]

Speaking hypothetically, is it theoretically possible for MCT to be an SSTO?

There were quotes from Elon that the F9 first stage can reach orbit with a very minor payload.
There also are some estimates that the first stage of F9 can do close to 9km/s dV.
So an SSTO with current F9 technology seems possible, but not practical.

Let's say it is possible to design MCT as an SSTO that can lift a payload in the F9-F9H range, which can also refuel in orbit. So basically you have a single common system that can launch from Earth, land on Mars, and come back.
The plane-like operation seems appealing because of the possible reduced complexity.

Is such a system even theoretically possible?
How large does it need to be to lift a payload in the F9-FH range?

[hkultala]

Speaking hypothetically, is it theoretically possible for MCT to be an SSTO?

There were quotes from Elon that the F9 first stage can reach orbit with a very minor payload.
There also are some estimates that the first stage of F9 can do close to 9km/s dV.
So an SSTO with current F9 technology seems possible, but not practical.

Let's say it is possible to design MCT as an SSTO that can lift a payload in the F9-F9H range, which can also refuel in orbit. So basically you have a single common system that can launch from Earth, land on Mars, and come back.
The plane-like operation seems appealing because of the possible reduced complexity.

Is such a system even theoretically possible?
How large does it need to be to lift a payload in the F9-FH range?

SSTO is different than SSTO+landing.

And in addition to the mass fraction needed for the delta-v is SSTO, there are many other inefficiencies:

Engines made for takeoff from earth are very unoptimal for doing anything else than taking of from earth;
There is just way too much thrust (unnecessary heavy engines, and maybe also too high acceleration with fuel tanks almost empty), and the nozzle is optimized for wrong wrong air pressure for most part of the flight.

No, it does not make any sense for MCT to have the T/W ratio and sea level nozzles required to take off from earth. On the other hand, same nozzle and same T/W ratio work for both liftoff from mars and upper stage from earth.

[Robotbeat]

Yes it's possible. Essentially Delta Clipper. (paging HMXHMX...)

I'd argue that given what SpaceX are attempting, this would be less efficient. But yes it could be done.

Musk has said it'd basically be a two-stage rocket, with a BFR and BFS. Or think about BFS as the payload doing a lot of the work to get to orbit.

[nadreck]

Yes it's possible. Essentially Delta Clipper. (paging HMXHMX...)

I'd argue that given what SpaceX are attempting, this would be less efficient. But yes it could be done.

Musk has said it'd basically be a two-stage rocket, with a BFR and BFS. Or think about BFS as the payload doing a lot of the work to get to orbit.

Getting to orbit is a possibility, but a functional BFR first stage does not need the TPS of the BFS/MCT/Tanker stage and a perfectly good first stage would be being disposed of by putting it in orbit as it could not be recovered. The limits seem to be about 1000m/s of atmospheric entry speed. Currently the F9 first stage can be travelling anywhere between 2000m/s and 6000m/s when the 2nd stage separates, however at 2000m/s it can expend another 3200-3500 m/s and return to the launch site and still have fuel to slow down and land, if instead it is moving at 4000m/s it probably only has enough ΔV to slow it down to a safe entry speed and land down range. At 6000m/s it has no propellant left at all. In all of these cases except the last one, it needs to perform retropulsion from whatever speed it is going to 1000m/s or less as it hits the thicker atmosphere

[M_Puckett]

Speaking hypothetically, is it theoretically possible for MCT to be an SSTO?

There were quotes from Elon that the F9 first stage can reach orbit with a very minor payload.
There also are some estimates that the first stage of F9 can do close to 9km/s dV.
So an SSTO with current F9 technology seems possible, but not practical.

Let's say it is possible to design MCT as an SSTO that can lift a payload in the F9-F9H range, which can also refuel in orbit. So basically you have a single common system that can launch from Earth, land on Mars, and come back.
The plane-like operation seems appealing because of the possible reduced complexity.

Is such a system even theoretically possible?
How large does it need to be to lift a payload in the F9-FH range?

Stretch it (the BFR first stage) and make it a tanker to fill a depot.

That is your most structurally efficient way to carry a meaningful payload.  Plus if ups your launch cadence using the same facilities as the MCT.

The residual prop minus what you need to deorbit and land are your payload.

[sanman]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

[john smith 19]

Speaking hypothetically, is it theoretically possible for MCT to be an SSTO?

There were quotes from Elon that the F9 first stage can reach orbit with a very minor payload.
There also are some estimates that the first stage of F9 can do close to 9km/s dV.
So an SSTO with current F9 technology seems possible, but not practical.

Let's say it is possible to design MCT as an SSTO that can lift a payload in the F9-F9H range, which can also refuel in orbit. So basically you have a single common system that can launch from Earth, land on Mars, and come back.
The plane-like operation seems appealing because of the possible reduced complexity.

Is such a system even theoretically possible?
How large does it need to be to lift a payload in the F9-FH range?

Your missing a few points.

Vertical take off Single Stage to orbit has been possible for decades.

The issues have been a)You loose 2/3 to 3/4 of the TSTO payload b)The stage (not a capsule) has to handle the full -7900ms delta v to land again c) This is the Mars Colony/i] transporter, which IIRC Musk has said  is in the 100 passenger (IE small airliner) category.

For the SSTO question b) is probably the killer. The amount of KE you need to dump rises at the square of the velocity. What's X at 2000 m/s is 16x that at about 8000 m/s in round numbers.

the notion the engine bells would survive that temperature becomes very doubtful. Likewise the amount of TPS you're going to ablate away on every single landing is likely to be considerable. 

All multiplied together there is no just not a good reason to do this.

[nadreck]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

and didn't cary a payload

[Robotbeat]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

and didn't cary a payload

No, it definitely could carry a payload, but it'd be significantly smaller than F9 can do with an upper. Plus it'd be expended.

[HMXHMX]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

and didn't cary a payload

The payload would be between 0 and 10K lbm depending on assumptions.

[nadreck]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

and didn't carry a payload

The payload would be between 0 and 10K lbm depending on assumptions.

The assumptions I am making bring it to zero *wink*

Seriously to get between 0 and 10k lbm you are throwing away the stage as compared to putting up more than 4 times the maximum there if recover the stage and only throw away a 2nd stage. That 0 to 10k lbm you mention would have to include all margins for any other purpose than getting to low orbit as well as a hypothetical payload.

[Exastro]

Suppose you were free to tweak the stage design to increase the payload? 

Without the US, interstage, payload, or fairing, the T/W should be a fair bit higher.  So you might gain by stretching the stage.  Or replacing the center engine with an MVac, which might be started only after the stage reaches near-vacuum. 

I realized it's unlikely that the stage would be able either to land or carry enough payload to compete with a normal F9 for cost/kg.  But suppose the stage itself had some value -- refuel it with several FH flights and it could push a big payload to TLI, TMI, or elsewhere, say.  Of course you'd need to tweak it some more to be able to do that. 

[HMXHMX]

Didn't Musk comment that F9 booster would be capable of SSTO if it didn't have to carry an upper stage on top.

and didn't carry a payload

The payload would be between 0 and 10K lbm depending on assumptions.

The assumptions I am making bring it to zero *wink*

Seriously to get between 0 and 10k lbm you are throwing away the stage as compared to putting up more than 4 times the maximum there if recover the stage and only throw away a 2nd stage. That 0 to 10k lbm you mention would have to include all margins for any other purpose than getting to low orbit as well as a hypothetical payload.

I wasn't making an economic case.  Only pointing out what the payload of an expendable SSTO based on  the SpaceX technology might be, in contravention of the comment that it couldn't carry any payload.

[llanitedave]

Why?  What purpose would it serve?

[bioelectromechanic]

It seemed counter inutitive for a fully reusable design to have 2 sets of landing legs, heat shields, avionics, engines, tanks, etc.

Interesting that it actually might be possible, even though only to LEO.

[su27k]

Why?  What purpose would it serve?

So that they can retire F9/FH after MCT came online.

A lot of people didn't read OP's question carefully, this is not about using F9 1st stage or any 1st stage to SSTO, the question is specifically asked about MCT, i.e. the 2nd stage of BFR, which should already have the TPS for reentry built-in.

[john smith 19]

It seemed counter inutitive for a fully reusable design to have 2 sets of landing legs, heat shields, avionics, engines, tanks, etc.

Interesting that it actually might be possible, even though only to LEO.

What's counter intuitive?

That you need 2 stages or that you need landing legs, avionics and heat shields for both?

[Hotblack Desiato]

From what I have gathered, MCT is supposed to be an SSTO.

Just not on Earth, where it needs to have a second stage, and in an environment where it is not supposed to carry a large payload (on Mars, MCT has to bring cargo down to the surface, not up into orbit).

[Elmar Moelzer]

b)The stage (not a capsule) has to handle the full -7900ms delta v to land again

Not sure what you mean with this point. Can you please elaborate on that?

[john smith 19]

b)The stage (not a capsule) has to handle the full -7900ms delta v to land again

Not sure what you mean with this point. Can you please elaborate on that?

A stage has much increased surface area, a fair chunk of which will be in the direct path of the airstream, as opposed to a capsule, where quite a lot of it is in the lee of the airstream.

Check the skin temperature maps of Apollo. Peak temperatures were a very small patch on the edge between main heat shield and the lee cone IE the most forward leading edge part of the structure. Outside of this patch temperatures dropped fast.

I've sometimes wondered if you could move that heat to leeward areas is there enough leeward area that you could dump the heat and keep the surface at a reasonable temperature.

If so you could have a semi passive heat pipe TPS.