DIRECT v3.0 - Thread 1

[NUAETIUS]

I have read that part of the Direct plan is to allow ATK to continue to develop the 5 segment SRB.

How does the SRB failure issue effect the idea of the manned Jupiter using the 5 segment SRB.  Seems that the 5 segment SBR would move the failure closer to the capsule, and cause a 20 percent increase in the power of the failure.

Could this kill  Ares I, a man rated Ares V (which some are talking about now) with it's 5.5 segment SRB, and Jupiter heavy manned with the 5 segment SRB?

[kraisee]

Interesting - your AIAA 2007 paper talks about using depot to overfuel the EDS for a 10% margin on the TLI.

I guess later analysis has shown more benefit in reducing stresses on the TLI engines by keeping the burn as short as possible?

Its more about maximizing performance.

When no depot is used, you maximize performance by dumping any excess mass overboard prior to TLI.

But if a Depot is involved, you can still meet all your performance targets *AND* still be able to add an additional margin as well.   That's a nice feature of that architecture.

Ross.

[Ben the Space Brit]

How does the SRB failure issue effect the idea of the manned Jupiter using the 5 segment SRB.  Seems that the 5 segment SBR would move the failure closer to the capsule, and cause a 20 percent increase in the power of the failure.

The problem in hand is that the Orion LAS is unable to get the Orion far enough away from the Ares-I core to avoid the parachutes being destroyed by falling hot debris from the self-destruct of the core.  The implications for SDLV, both Side-mount and In-line, are being analysed at the moment.  The possibility exists that, as the aerodynamic forces acting on Orion on Ares-V, DIRECT and NSC are lower (by about 33%) than they are on Ares-I, the LAS might get the Orion clear of the pyrotechnic debris cloud.  A lot depends on the exact figures of the minimum safe distance, both for the debris cloud and the detonation shockwave from the range safety destruction of the liquid-fuelled component of the launch vehicle.

Worst comes to worst, NASA defaults to Atlas-V Phase 2 and 3 with Delta-IVH+ as the interim launcher until the two big Atlases are ready.

[kraisee]

luke & lancer,
Can I ask you guys to start a specific spin-off thread to discuss the model rockets?

The discussion is great and I've been following along closely myself (one day I'd like to build one of these myself!) but we have a hard enough time justifying that DIRECT isn't a 'paper rocket' without including discussion here of real 'paper rockets'!    It could very easily lead a newcomer to the concept to the wrong conclusion.

This concern goes away if it gets its own dedicated thread

Ross.

[kraisee]

I have read that part of the Direct plan is to allow ATK to continue to develop the 5 segment SRB.

Not really.   We would prefer to save the money and just keep using the current Shuttle-spec 4-segs instead.

Having said that though, we do acknowledge that there is a purely political pork element which might mean we can't avoid the 5-seg boosters.

How does the SRB failure issue effect the idea of the manned Jupiter using the 5 segment SRB.  Seems that the 5 segment SBR would move the failure closer to the capsule, and cause a 20 percent increase in the power of the failure.

That's correct.   The top of the 'active' part of the SRB would be located about 8 meters closer than at present.   And yes, the larger the booster, the more propellant and structure would be involved in such an explosion -- which does increase the potential danger somewhat.

Could this kill  Ares I, a man rated Ares V (which some are talking about now) with it's 5.5 segment SRB, and Jupiter heavy manned with the 5 segment SRB?

I think its a showstopper for Ares-I, but not for Ares-V or Jupiter.

Ross.

[brihath]

Ross-

A while back you mentioned a "showstopper" for Ares I, and as I recall, you stated the abort scenario was not the issue, but rather, something else.

I was curious when this other showstopper will be discussed, and where it will be posted.  Will it go on the Ares I development thread?

Thanks.

[Drapper23]

Ross, What would happen to the SDHLV(NSC) launched Orion if there is a solid rocket booster failure? Is the USAF solid rocket booster failure study also a showstopper for the SDHLV(NSC)?

[MP99]

Interesting - your AIAA 2007 paper talks about using depot to overfuel the EDS for a 10% margin on the TLI.

I guess later analysis has shown more benefit in reducing stresses on the TLI engines by keeping the burn as short as possible?

Its more about maximizing performance.

When no depot is used, you maximize performance by dumping any excess mass overboard prior to TLI.

But if a Depot is involved, you can still meet all your performance targets *AND* still be able to add an additional margin as well.   That's a nice feature of that architecture.

Ross.

It seem strange to me that 10% additional fuel from a depot is margin, but 2.9% additional fuel which was unused ascent FPR is a burden.

More fuel for the same burnout mass will give you more delta-V, and therefore margin. Whilst I can understand concerns that a longer burn puts more strain on the engine, depot architecture can handle much higher payloads, which would increase burn times substantially.

I thought the "Pre-TLI Overboard Mass" was boiloff (the figure listed on the J-246 EDS sheet would give you nearly 8 days of loiter @ 0.35% per day)?

cheers, Martin

[robertross]

I think the question which really needs to be answered regarding exploding SRB's, is exactly *how* they come apart.

An SRB has a lot more area on the sidewalls than on the top/bottom.   My question is that in the event of a severe over-pressurization, do those 'sides' blow out sideways, or all around?

That report seems to suggest they make a large 'ball', but they also say that's just an assumption and that the camera angle doesn't really allow a precise analysis.

But I think we really need to see some real analysis before relying upon that assumption though.

If 80-90% of the structures is actually blown "sideways" instead of up/downwards, that will alter the danger levels.

Ross.

There are a few other models, combinations of the two you have shown, which would occur more prevelantly. For one case, move the centered explosion model to just below the nose cap, so it occurs further up. This is closer to a worst case (though not actually).

For this assumption, the ET attachement point is stronger, so the likelyhood of a rupture there is more remote than 180 degrees away, and slightly above or below the joints/rings.

Once the case ruptures, say opposite the upper SRB-ET attachment point, the 'explosion' expands the case outwards, relieving the internal pressures to the atmosphere. This adjusts the trajectory of the rocket to the left (port). If the TVC system cannot compensate, or the SSME gimbaling system, the differential forces could cause vehicle breakup. Now it 'hinges' on the strength of the ET-SRB attachment point. If this gives way, the SRB would fall away from the ET as the TVC is pointing the opposite way to compensate for the blowout forces at the top.

If at this point there is still sufficient pressure to propogate the 'explosion', the weakest point would likely be at the blowout point (though structural fatigue could cause a break at the mid-point). So now the SRB is ripping apart at the top, possibly blowing the nose cap towards the Orion, along with the hot gases.

How much of the resulting fireball & AP chunks reaches the capsule I cannot speculate, but the failure modes of the SRB are many and varied, and each presents unique issues (like ET impingement also causing an LH2/LOX fireball).

An approach to reduce SRB forward momentum during an abort would be to drop the throat/skirt as a module. Now you no longer can generate as much thrust, helping the cause.

Of course this all should be discussed in a new Direct abort thread.

[robertross]

I thought the report concluded that it was *radiative* heating that destroyed the chutes.  If so, being ahead of the debris cloud doesn't necessarily bring you to safety.  A large and hot debris cloud can radiate a lot of heat.

Better make sure the chutes are white.

Are you sure??? We DO want to find this capsule... 

Perhaps a thin reflective mylar nano-coating would be better.

[kraisee]

Ross-

A while back you mentioned a "showstopper" for Ares I, and as I recall, you stated the abort scenario was not the issue, but rather, something else.

I was curious when this other showstopper will be discussed, and where it will be posted.  Will it go on the Ares I development thread?

Thanks.

I think you're actually referring to the Showstopper for Not-Shuttle-C -- which was the Abort motor always rupturing the LOX Tank above, and in close proximity to, the Orion.

With this latest SRB report, I'm actually even more concerned about the Not-Shuttle-C placing the Orion so much closer to the SRB's too, but that's a side issue (excuse the pun).

The only real 'showstoppers' which I'm aware of with Ares-I is that it a) has not been an affordable proposition at any time of its existence, b) a crewed Ares-I will never actually fly until at least 7 years after Shuttle has retired -- even if CxP cuts the test program down to nothing and increases risks at every level by doing so, and c) it has such p*ss-poor performance that its margins are nothing but a very bad joke.

But, other than that, its fine...   

Ross.

[cixelsyD]

Out of curiousity, could  it be possible to just drop Ares I and go straight to EELV? I mean lets say dragon is ready to liftoff in 2012, even though it can't lift orion, can it be modified to still be useful for moon missions?

I don't think it's the best way, but it would be interesting, this is highly reliant on spacex, if they have a problem expect massive delays in everything...

Edit: Big error, said F9 instead of Ares I

[cixelsyD]

Made a typo in the last post I made , changed it...

What makes something into a lunar capsule, I mean they both don't touch the surface of the moon, is it just based on how many supplies can be carried?

[brihath]

I think you're actually referring to the Showstopper for Not-Shuttle-C -- which was the Abort motor always rupturing the LOX Tank above, and in close proximity to, the Orion.

With this latest SRB report, I'm actually even more concerned about the Not-Shuttle-C placing the Orion so much closer to the SRB's too, but that's a side issue (excuse the pun).

The only real 'showstoppers' which I'm aware of with Ares-I is that it a) has not been an affordable proposition at any time of its existence, b) a crewed Ares-I will never actually fly until at least 7 years after Shuttle has retired -- even if CxP cuts the test program down to nothing and increases risks at every level by doing so, and c) it has such p*ss-poor performance that its margins are nothing but a very bad joke.

But, other than that, its fine...   

Ross.

Aaahhh....that's right, it was NSC.

I guess Ares I is OK with the exception of the "minor issues" you cited!  (LOL)

[marsavian]

Made a typo in the last post I made , changed it...

What makes something into a lunar capsule, I mean they both don't touch the surface of the moon, is it just based on how many supplies can be carried?

Whether the heat shield can take an Earth re-entry from a Lunar Orbit.

[Ben the Space Brit]

What makes something into a lunar capsule, I mean they both don't touch the surface of the moon, is it just based on how many supplies can be carried?

There are a number of differences between LEO-only and lunar-capable spacecraft;

1. Life support & consumables - The free-flying mission length jumps from three or four days (ISS crew rotation) to 7-14+ days (lunar free-return or seven-day+ expedition);

2. Shielding - Outside of Earth's magnetosphere, the spacecraft will need better radiation shielding as nothing will be there to protect it from the Solar Wind and cosmic rays.  Additionally, it will need better thermal protection as there will be continual exposure to sunlight rather than a 45 minute day followed by a 45 minute night;

3. Propulsion - Some provision must be made for high-energy manoeuvres in deep space such as orbital insertion burns, plane change burns and other mid-course corrections; Either a powerful MPS on the spacecraft (like the hypergolic Apollo SPS engine) or a long-lifespan propulsion module (like the LH2/LOX Centaur);

4. Room to manoevure - Any flight over 7 days will seriously need to give the crew room to exercise and get out of each other's hair.  When the Apollo missions were in the early stages of being planned, the crew were going to stay in the CM for the entire flight to the Moon, only opening up the LEM for initial checks and then leaving it closed until after LOI; in practice, the LEM was used as an extended living area.  In mission durations >30 days, there would also need to be exercise equipment to ensure that the crew do not suffer serious muscle and bone degradation;

5. Heat shield - Re-entry from Return Orbit from the Moon is a lot more energetic than re-entry from LEO.  The heat sheild would either need to be thicker or be made of a tougher material.  Additionally, a space plane-style vehicle (such as the Dream Chaser) might even be unsuitable because the large re-entry heatshield would be vulnerable to interplanetary MMOD impacts.

Ironically, Orion has already lost several of the above features to fit onto Ares-I.  Putting them back in is one of the attractions of a heavier launch vehicle like the Jupiter family and the SDHLV.

[Tez]

Interesting - your AIAA 2007 paper talks about using depot to overfuel the EDS for a 10% margin on the TLI.

I guess later analysis has shown more benefit in reducing stresses on the TLI engines by keeping the burn as short as possible?

Its more about maximizing performance.

When no depot is used, you maximize performance by dumping any excess mass overboard prior to TLI.

But if a Depot is involved, you can still meet all your performance targets *AND* still be able to add an additional margin as well.   That's a nice feature of that architecture.

Ross.

It seem strange to me that 10% additional fuel from a depot is margin, but 2.9% additional fuel which was unused ascent FPR is a burden.

More fuel for the same burnout mass will give you more delta-V, and therefore margin. Whilst I can understand concerns that a longer burn puts more strain on the engine, depot architecture can handle much higher payloads, which would increase burn times substantially.

I thought the "Pre-TLI Overboard Mass" was boiloff (the figure listed on the J-246 EDS sheet would give you nearly 8 days of loiter @ 0.35% per day)?

cheers, Martin

I think it's probably because the "10%" is delivered by another vehicle whereas the "2.9%" is a load on the Jupiter first stage.

Then again my rocket science is based on bottles.

[winkhomewinkhome]

A question for anyone who wishes to answer.

If "we" are able to carry with us additional fuel supply to the moon, might we have enough that on the return to Earth that the mission not need to immediately enter the atmosphere, but rather reenters Earth orbit, and then lands when and where it wants?

hopefully that makes some degree of sense???  Thank you!

By the way - Ross, great job on NPR - as everyone else has stated!

[brihath]

A question for anyone who wishes to answer.

If "we" are able to carry with us additional fuel supply to the moon, might we have enough that on the return to Earth that the mission not need to immediately enter the atmosphere, but rather reenters Earth orbit, and then lands when and where it wants?

hopefully that makes some degree of sense???  Thank you!

By the way - Ross, great job on NPR - as everyone else has stated!

Others will probably answer with more details, but the velocity change needed to enter earth orbit on a Lunar return would require a velocity change similar to a TLI burn on the outbound leg.  In Apollo, that velocity change was handled during atmospheric reentry.  Depending on mass it could be a substantial amount of fuel.

[Jorge]

A question for anyone who wishes to answer.

If "we" are able to carry with us additional fuel supply to the moon, might we have enough that on the return to Earth that the mission not need to immediately enter the atmosphere, but rather reenters Earth orbit, and then lands when and where it wants?

hopefully that makes some degree of sense???  Thank you!

By the way - Ross, great job on NPR - as everyone else has stated!

Others will probably answer with more details, but the velocity change needed to enter earth orbit on a Lunar return would require a velocity change similar to a TLI burn on the outbound leg.  In Apollo, that velocity change was handled during atmospheric reentry.  Depending on mass it could be a substantial amount of fuel.

It will be a substantial amount of propellant in any case. You need to carry with you not just the prop needed to brake back into LEO, you also need the prop to accelerate *that* prop back toward Earth from lunar orbit, then the prop needed to decelerate *that* prop into lunar orbit...

It's an exponential problem, and I guarantee the prop mass would end up far, far higher than the mass of the heat shield.