Falcon Heavy Demo Mission Payload Speculation

[Jim]

It does none of those things as explained before.  Dragon is not flying in a fairing.

Which explanation are you referring to? Are you saying Dragon could not be launched in a fairing?

It isn't as simple as other payloads.  It would require many one off modifications.

[envy887]

Why would it need a parachute?

To eliminate tanks, legs, and landing thrusters, e.g. to use a Dragon 1 (of which they have surplus) instead of a Dragon 2. Though perhaps it could use Dragon's chutes, if they just want to fish it out of the drink like the last fairing.

How do you know extra TPS is required? It might be required on the PAF, but the side walls would be well away from the radiant heat of the hypersonic bow shock.

The entire Shuttle was covered in TPS because temps even on the backshell were high enough to cause aluminum to lose almost all it's strength. The stage will have the same issue - although SpaceX isn't planning to fly this one again, so they might not care and are probably willing to take a chance that it doesn't make it through peak heating.

Why would it would need rear flaps? The Dragon2 has thrusters and a moveable mass.

Flaps can generate several orders of magnitude more control torque than all the Dracos on Dragon, and they can make it more passively stable. Though if they mount a whole Dragon on the PAF it's likely front-heavy enough to be stable already.

Whilst I agree that something along the lines of the existing Dragon to trunk fittings could be used to mount the payload adapter, why do they need to show that working on the demo flight? Wouldn't simply recovering the stage be a huge achievement?

They will have to demo it eventually. Maybe they can convince a paying customer to be they guinea pig when they do.

I suppose the idea of an upside down Dragon is more than silly enough to qualify, and just might work as a "hail mary" with a normal second stage.

[envy887]

It does none of those things as explained before.  Dragon is not flying in a fairing.

Which explanation are you referring to? Are you saying Dragon could not be launched in a fairing?

It isn't as simple as other payloads.  It would require many one off modifications.

What mods would it require to fly just a Dragon 1 pressure shell and TPS mounted upside down on the PAF?

- A one-off PAF to CBM adapter, for sure
- Some one-off way for the second stage to control the chutes, if those will be used.
- Perhaps a way for the second stage to get data off any required instrumentation on Dragon.

Dragon shouldn't need power or conditioned air inside if the ECLSS is turned off or removed and all the electronics are powered down. It also wouldn't need the trunk for power or cooling with nothing inside to power or cool. No need for data or telemetry for the same reasons. It's just a dumb payload at that point - it can be encapsulated and mated like any payload.

The second stage would provide the avionics, telemetry, and control systems, just like a commsat launch.

[coal_burner]

what if they were to build an instrumented boilerplate 2nd stage with a heat shield, thrusters, and just an mvac mockup, and carried that up inside the payload fairing.

that would allow them to get data on a cylindrical reentry vehicle without the risk of a 2nd stage failure due to reentry modifications.

I'm pretty sure that launching a 2nd stage on top of a 2nd stage counts as pretty silly.

The current second stage is about twice as long as anything that will fit in the fairing, so a boilerplate upper stage launched faired wouldn't look or fly like the real thing.

if a falcon 2nd stage tank is only 9.3 m long and the fairing can support a payload which is 11.4 meters long, it seems like everything should fit just fine so long as you dont have the mvac vacuum nozzle extension installed.
since it is so thin, i doubt it would survive reentry anyway due to flutter.
i think they would jettison it before reentry anyway.

[envy887]

what if they were to build an instrumented boilerplate 2nd stage with a heat shield, thrusters, and just an mvac mockup, and carried that up inside the payload fairing.

that would allow them to get data on a cylindrical reentry vehicle without the risk of a 2nd stage failure due to reentry modifications.

I'm pretty sure that launching a 2nd stage on top of a 2nd stage counts as pretty silly.

The current second stage is about twice as long as anything that will fit in the fairing, so a boilerplate upper stage launched faired wouldn't look or fly like the real thing.

if a falcon 2nd stage tank is only 9.3 m long and the fairing can support a payload which is 11.4 meters long, it seems like everything should fit just fine so long as you dont have the mvac vacuum nozzle extension installed.
since it is so thin, i doubt it would survive reentry anyway due to flutter.
i think they would jettison it before reentry anyway.

The fairing can't hold an object that is 11.4m long AND 3.66m in diameter it's whole length. And the stage is much longer than 9 meters. The tanks alone are nearly 10 meters end to end and the engine adds another 5 meters.

[coal_burner]

what if they were to build an instrumented boilerplate 2nd stage with a heat shield, thrusters, and just an mvac mockup, and carried that up inside the payload fairing.

that would allow them to get data on a cylindrical reentry vehicle without the risk of a 2nd stage failure due to reentry modifications.

I'm pretty sure that launching a 2nd stage on top of a 2nd stage counts as pretty silly.

The current second stage is about twice as long as anything that will fit in the fairing, so a boilerplate upper stage launched faired wouldn't look or fly like the real thing.

if a falcon 2nd stage tank is only 9.3 m long and the fairing can support a payload which is 11.4 meters long, it seems like everything should fit just fine so long as you dont have the mvac vacuum nozzle extension installed.
since it is so thin, i doubt it would survive reentry anyway due to flutter.
i think they would jettison it before reentry anyway.

The fairing can't hold an object that is 11.4m long AND 3.66m in diameter it's whole length. And the stage is much longer than 9 meters. The tanks alone are nearly 10 meters end to end and the engine adds another 5 meters.

thanks for the cool pictures.
i toom my tank dimensions off the modeling forum, so i was working under the assumption that the tanks were over 2 meters shorter than they actually are.

[Jim]

What would be the simplest way to provide this configuration from existing parts?

One alternative would be to use an existing Dragon, possibly outfitted with Super Draco engines for landing, fixed to the PAF, enclosed in the payload fairing.

I didn't even see the drawing when I first responded.
My comment was just in placing a Dragon in the fairing in the normal orientation.

Now you want to flip it?  That is so far from simple.  And certainly doesn't do any of the following?

using the Dragon2 to provide all of this functionality massively simplifies the problem, and does so in the shortest possible timeframe.

What says that the whole vehicle can loads in that direction?

What says that anything in the nose area can take the interface loads?

[envy887]

What says that the whole vehicle can loads in that direction?

What says that anything in the nose area can take the interface loads?

I'm sure SpaceX FEA analysis and structural article testing would say if it's possible.

I have no idea if they have already done that analysis or how much work it would take to do it. But I'm sure that somewhere in the Dragon design requirements are specifications for the required loads in that direction and through that interface.

[OneSpeed]

What says that the whole vehicle can loads in that direction?

What says that anything in the nose area can take the interface loads?

I'm sure SpaceX FEA analysis and structural article testing would say if it's possible.

I have no idea if they have already done that analysis or how much work it would take to do it. But I'm sure that somewhere in the Dragon design requirements are specifications for the required loads in that direction and through that interface.

I haven't attempted the finite element analysis either, and given this is a speculative thread, I'm not likely to try. However, I should point out that Dragon is a pressure vessel, and so the entire capsule would have been designed to handle some maximum value of pressure. The walls and internal ribbing might be slightly thicker near stress concentrators, so the nose might not be especially weak. Also, when mating to a fixed annulus, the best shape to distribute the load would be a truncated cone, the same as the nose of the capsule. It might even be worth running the capsule at a higher internal pressure than normal, in order to minimise compressive loading on the capsule walls.

[Jim]

I have no idea if they have already done that analysis or how much work it would take to do it. But I'm sure that somewhere in the Dragon design requirements are specifications for the required loads in that direction and through that interface.

yes, and what says there are requirements for loads as high as these.

[Jim]

I haven't attempted the finite element analysis either, and given this is a speculative thread, I'm not likely to try. However, I should point out that Dragon is a pressure vessel, and so the entire capsule would have been designed to handle some maximum value of pressure. The walls and internal ribbing might be slightly thicker near stress concentrators, so the nose might not be especially weak. Also, when mating to a fixed annulus, the best shape to distribute the load would be a truncated cone, the same as the nose of the capsule.

Pressure has nothing to do with it or the walls of the vehicle.  What says loads on the docking interface can take 3-6 g's load of the whole capsule. Not to mention the dynamic loads of ascent.

. It might even be worth running the capsule at a higher internal pressure than normal,

No, that is exactly something they would not do.  That would take analyses and hardware changes that have no other future use.

[envy887]

I have no idea if they have already done that analysis or how much work it would take to do it. But I'm sure that somewhere in the Dragon design requirements are specifications for the required loads in that direction and through that interface.

yes, and what says there are requirements for loads as high as these.

The docking standard includes an axial compression spec of 300 kN because Altair was going to use it to push Orion around. That's 6 gees on a 5000 kg capsule, quite a bit more than what an empty Dragon with no trunk or fuel masses.

Obviously that doesn't include vibe and non-axial loads which are probably worse on a LV going through the atmosphere. But it's about the right ballpark if SpaceX planned Dragon+F9 upper stage to have the capability to push anything around.

FH also has plenty of performance to deal with the throttling losses to keep the acceleration under 3g if needed.

[andyr]

Just send a previously flown Dragon into the solar system for eternity.

[sevenperforce]

Just send a previously flown Dragon into the solar system for eternity.

Not gonna be recovering the second stage if they do that!

[rklaehn]

I think given the payload of the first dragon and the payload capability of the falcon heavy, it is pretty clear what the payload is going to be:

[Jim]

The docking standard includes an axial compression spec of 300 kN because Altair was going to use it to push Orion around. That's 6 gees on a 5000 kg capsule, quite a bit more than what an empty Dragon with no trunk or fuel masses.

Meaningless.  Not applicable to Dragon.

FH also has plenty of performance to deal with the throttling losses to keep the acceleration under 3g if needed.

not going to happen

[hkultala]

Of course it will be a school bus. Elon has been talking how his fairing is large enough for a school bus.

[Robotbeat]

Maybe the payload will simply be the reusable upper stage (plus a small token payload), giving as much propellant as possible to assist recovery.

[dror]

Maybe the payload will simply be the reusable upper stage (plus a small token payload), giving as much propellant as possible to assist recovery.

I'd think they need to prove the vehicle performance to some extent so a payload whithin F9 ability or smaller than STP2 would not suffice.

[guckyfan]

Maybe the payload will simply be the reusable upper stage (plus a small token payload), giving as much propellant as possible to assist recovery.

I'd think they need to prove the vehicle performance to some extent so a payload whithin F9 ability or smaller than STP2 would not suffice.

Plenty of propellant to ballast the stage for Merlin landing would count as payload too.