Author Topic: MCT Speculation and Discussion Thread 4  (Read 624387 times)

Online Elmar Moelzer

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Re: MCT Speculation and Discussion Thread 4
« Reply #2500 on: 07/31/2016 09:15 PM »
I would assume that the DC-X or subsequently the Delta Clipper would have had the same problem with nose first entry. IIRC, the DC-X demonstrated it to work just fine.

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2501 on: 07/31/2016 09:30 PM »
A reusable second stage would be actively guided it its landing zone, just like the first stage. No need to drop it in the ocean. It could land back at the launch site or on a barge.

BTW, this is the MCT speculation thread, so why are we having what seems to be a F9/FH discussion?

Agreed, it's in the wrong thread, I suspect it spun off the Raptor powered upper stage discussion. It should probably be moved.

Whilst the stage could be actively guided in the landing zone, for a GEO launch, the zone itself would be determined by the highly elliptical orbit after launching the satellite, and how quickly that orbit decayed. It can take years for that to happen, so there probably wouldn't be any fuel left for landing.

Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #2502 on: 08/01/2016 12:02 AM »
A reusable second stage would be actively guided it its landing zone, just like the first stage. No need to drop it in the ocean. It could land back at the launch site or on a barge.

BTW, this is the MCT speculation thread, so why are we having what seems to be a F9/FH discussion?

Agreed, it's in the wrong thread, I suspect it spun off the Raptor powered upper stage discussion. It should probably be moved.

Whilst the stage could be actively guided in the landing zone, for a GEO launch, the zone itself would be determined by the highly elliptical orbit after launching the satellite, and how quickly that orbit decayed. It can take years for that to happen, so there probably wouldn't be any fuel left for landing.

If it is designed as a reusable stage then it would have enough fuel to deorbit and land. It's a tall order to have that much fuel and a usable payload, so that's where a cargo version of the MCT system could come in handy.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2503 on: 08/01/2016 06:14 AM »
...
 it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry.
...

False. On a Dragon to ISS mission the residual propellent outweighs the entire second stage, and it only takes 1% of the initial 100 tonne propellent load to outweigh a Merlin.

At atmospheric drag will settle the remaining propellent in the nose long before it's significant enough to overpower the RCA thrusters, resulting in a quasi-stable configuration that cold be controlled by either RCS or small active aerodynamic surfaces during re-entry.

ISS missions have literal tons of unused margin, if your going to re-enter nose first with a heat shield then your not using propulsion until terminal landing so their is no reason for the vehicle to have tons of excess propellant unless you have intentionally kept it for ballast.

In an engine first re-entry your burning propellant during entry and losing mass and you have to remain stable all the way through that burn which means you need to be stable with your burnout quantity of propellant, not just the initial propellant.

Lastly the engine mass here is going to be a Raptor which is certainly going to have a higher mass then a Merlin, also propellant is at a minimum in two tanks so propellant center of mass can never be fully up at the nose.  Propellant tanks structures and engine intakes are designed for propellant at the bottom of the tank, if its gone to the nose the engine will not be able to start.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2504 on: 08/04/2016 04:43 AM »
Here is my idea of BFR and MCT. The major idea is I am predicting that MCT will not have heat shield, except MCT Escape module for emergency situation.
MCT will shield engine compartment using low thrust to create buble and push heated air from engine compartment.
it will avoid to build 15 m heat shield, or complicated maneuver during landing using MCT Escape module heat shield and then turn around for braking and landing.

Offline Crispy

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Re: MCT Speculation and Discussion Thread 4
« Reply #2505 on: 08/04/2016 09:37 AM »
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #2506 on: 08/04/2016 10:52 AM »
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D

That idea comes from the concept of entering engines first. I am sure the mass of propellant would dwarf the weight of a heat shield, but a heatshield protecting the engines is tricky, especially if like on Mars you need to fire them supersonic.

To me it means you cannot enter engines first and have to find a solution to the stability and other problems, when entering nose first.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2507 on: 08/04/2016 06:00 PM »
Does the mass of the heat shield exceed the mass of the fuel required to create a sufficiently large "bubble" ?
Please show your working :D
Not but it will technologically and operation less complicated.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2508 on: 08/04/2016 06:27 PM »
MCT without heat shield for MCT Booster
« Last Edit: 08/04/2016 08:50 PM by raketa »

Online philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2509 on: 08/04/2016 06:41 PM »
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
« Last Edit: 08/04/2016 06:43 PM by philw1776 »
“When it looks more like an alien dreadnought, that’s when you know you’ve won.”

Online Elmar Moelzer

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Re: MCT Speculation and Discussion Thread 4
« Reply #2510 on: 08/04/2016 07:44 PM »
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
The MCT is currently assumed to be the second stage of a two stage LV. It will (probably) launch from mars as an SSTO, though.
They would get through the heat shield with a door.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2511 on: 08/04/2016 07:50 PM »
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew

How about like this?

It has to turn around for landing, I think retro propulsive braking test give them numbers that propulsion is good enough to build shield.

Offline raketa

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Re: MCT Speculation and Discussion Thread 4
« Reply #2512 on: 08/04/2016 08:52 PM »
Is this a SSTO?  How do you get enough Km/sec to reach LEO, etc?
How do humans get from the living area to/from escape pod with heat shield in between?
Just showing MCT. BFR is not part of this picture, but BFR still need it. By the way BFR will be use together with MCT just 0.0000019% MCT Mars flight.
« Last Edit: 08/04/2016 10:15 PM by raketa »

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2513 on: 08/04/2016 10:18 PM »
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.

Matthew

How about like this?

It has to turn around for landing, I think retro propulsive braking test give them numbers that propulsion is good enough to build shield.

The S2 doesn't have to turn around for landing. It could land on the inflatable, which would incidentally absorb some shock loading, as would the ocean.

SRP is only intended for the range from Ma5 to Ma1.5. The mass of fuel required to burn retro-propulsively for the entire EDL sequence would be vastly greater than the mass of a heatshield, and would severely limit the landed payload, if not eliminate it.

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2514 on: 08/05/2016 09:39 AM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

Offline OneSpeed

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Re: MCT Speculation and Discussion Thread 4
« Reply #2515 on: 08/05/2016 12:05 PM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

Sorry, I should have been clearer. I suspect there are (at least) two scenarios being discussed concurrently on the thread. One is the Earth EDL of a Raptor engined Falcon S2, possibly from a highly elliptical orbit after delivering a geosynchronous satellite, and the other is raketa's proposal for a BFS performing Mars EDL without a heatshield.

For the S2 I was suggesting a HIAD could remove the EDL fuel requirement entirely. For the BFS, which could be manned, I was suggesting that to achieve the ΔV for Mars EDL purely propulsively would require too much fuel for it to have any useful payload.

I hope this helps.
« Last Edit: 08/05/2016 01:35 PM by OneSpeed »

Offline Danny Dot

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Re: MCT Speculation and Discussion Thread 4
« Reply #2516 on: 08/05/2016 01:42 PM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.

Danny Deger

Offline JasonAW3

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Re: MCT Speculation and Discussion Thread 4
« Reply #2517 on: 08/05/2016 03:26 PM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.

Yeah, maybe, but they ain't gonna like it!

     Seriously though, the G tolerance will vary from person to person.  Assuming the average group of people, up to half of these people will likely be knocked unconscious, Some may have breathing issues, and a few may have heart issues due to the G load.  This is not even taking into account three to nine months of deconditioning from microgravity.

     Even with current exercise, drugs and therapy, there will be health issues that have to be compensated for during the descent.  25Gs may be the normal max that people can take, with minimal deconditioning, but I don't think we've ever had anybody come back to Earth after more than three months of microgravity at a 20G reentry.
My God!  It's full of universes!

Offline envy887

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Re: MCT Speculation and Discussion Thread 4
« Reply #2518 on: 08/05/2016 04:29 PM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

It still has to be shielded; it will be exposed to at least 60 seconds of plasma blast hotter than Raptor exhaust temps. It's going to be WAY hotter than a Falcon 9 S1 entry, which is already pretty toasty.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #2519 on: 08/05/2016 05:52 PM »
Don't assume the EDL takes as long as a manned capsules entry, deceleration can be VERY fast if your coming in steep it just makes for very high g-forces and a tank can tolerate that.

The crew can tolerate a 20G entry.
No, frankly.  They can't.  Check your sources.  We're talking about sustained G-loading that lasts tens of seconds at near-peak intensity, presumably with considerable additional vibration from the turbulence.  Per Wikipedia, "Only the most motivated volunteers were capable" of reaching this 20G level in testing for 10s duration with a steady centrifuge, and more than that is suggested to result in injury and/or LOC.

Call it 10G peak eyeballs-in and assume some of the crew will black out or come down with concussions.  For existing spacecraft like Soyuz, 8.2G is an emergency condition encountered only during a ballistic reentry, after something goes wrong with separation, and the Shuttle gets more like 3G.

Eyeballs-in may not always be perfectly achievable either.  A reusable lander has to decelerate at a variety of orientations, and it may not be weight-feasible to have a pivoting chair.  20G's applied for a very short time at a slight angle to eyeballs-in will cause a red-out or a black-out by pushing enough G's at a person in the wrong direction, where they have low tolerance.

I'm not even trying to take into account deconditioning;  A known unknown.  But there's too many reasons to be conservative with G-loading already.  If your mission needs 20G reentry, redesign your mission.
« Last Edit: 08/05/2016 06:03 PM by Burninate »

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