Author Topic: UK steps up, as ESA commit to ATV Service Module on NASA's Orion  (Read 375508 times)

Offline pippin

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Umm... Didn't Apollo use the same strategy? Actually using the same engine, too?

Offline woods170

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On a more positive note (from the same article), it looks like ESA has resolved the SM's excess weight issue:
Quote
ESA’s assurances followed a May 19 preliminary design review where Airbus officials showed they had resolved the module’s excess weight.

I thought the main issue was with the command module weight and its parachutes. How much overweight was the SM?
Half a metric ton.

Online Herb Schaltegger

Umm... Didn't Apollo use the same strategy? Actually using the same engine, too?

It did, but consider - the SLA panels created a decent amount of physical separation between the upper dome of the propellant tanks, even disregarding the presence or absence of an LM underneath. Of course, that being said, I can't imagine that the effect of the SPS firing off into an LM ascent stage loaded with hypergolic propellants would be too gentle.

But either way, it beats the alternative of remaining attached to an off-trajectory booster or one that is in the process of rapid, unplanned disassembly ...
Ad astra per aspirin ...

Offline woods170

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No.

The large engine nozzle in the centre (ex-Shuttle OMS engine) is for ascent abort situations. The smaller engines around the perimeter are for in-space delta-V manoeuvres (e.g. lunar orbit insertion, trans-Earth injection).

And anyway, ESA's lunar lander has been cancelled.

The OMS Engine?  For Ascent Abort?  Holy cats, anybody thought about what that's going to do to the oxidixer tank right beneith that thing?  I guess they want to save a bit of money on the self destruct of teh stack if they have to do an ascent abort.  Use the OMS engine to start a chain reaction explosion as it tries to get away from the rocket!  Did they at LEAST put a flame deflector on top of the tank to avoid the inevitable BOOM?
The OMS engine is used in certain phases of Ascent Abort scenarios. And yes, Apollo did the same thing, with the same possible risk coming from the stage directly underneath.

Also, simpl simon is slightly mistaken in his description of the use of the OMS engine:
The OMS engine is the primary engine for the larger delta-v manoeuvres such as lunar orbit insertion, trans-earth injection. Smaller delta-V manoeuvres are handled by the smaller engines around the perimeter. Those same smaller engines serve in a back-up role to handle the larger delta-v manoeuvres (such as trans-earth injection) in case the main OMS engine fails.
« Last Edit: 08/14/2014 01:07 pm by woods170 »

Offline pippin

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I don't really think a few feet of physical separation make a lot of difference in a closed interstage cone when you fire a rocket engine above.
Since this was (and is) part of the escape concept me thinks that they'd have looked into the effects the engine would have on the tank.
After all, the tank should be well cooled with LOX and if it disintegrates a few seconds after the separation due to over pressure it might not harm that much. They might even have breaking points to make sure it doesn't rupture at the top.
« Last Edit: 08/14/2014 01:08 pm by pippin »

Offline Proponent

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Umm... Didn't Apollo use the same strategy? Actually using the same engine, too?

It did, but consider - the SLA panels created a decent amount of physical separation between the upper dome of the propellant tanks, even disregarding the presence or absence of an LM underneath. Of course, that being said, I can't imagine that the effect of the SPS firing off into an LM ascent stage loaded with hypergolic propellants would be too gentle.

But either way, it beats the alternative of remaining attached to an off-trajectory booster or one that is in the process of rapid, unplanned disassembly ...

Isn't it likely that in this abort scenario Apollo would have used the SM's RCS quads to separate from the S-IVB before SPS ignition?  Wouldn't Orion likely do something similar?

EDIT:  Typos.
« Last Edit: 08/16/2014 04:23 am by Proponent »

Offline Ben the Space Brit

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Now, maybe I'm wrong, but the use of the Orion's MPS for abort will be exclusively after the LAS tower is jettisoned, right? That would be after they've gone past the 66-mile limit and are in space. In such an environment, there is no risk of an explosion (i.e. violent chemical reaction generating heat and rapidly expanding front of reaction product vapour).

The OPS's plume will cave in the LOX tank's top dome easily, no doubt. However, there wouldn't be an 'explosion', just a sudden, violent depressurisation of the tank. This would actually be useful because it would help push the spacecraft away from the booster.
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Offline Proponent

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Might not the sudden, violent depressurisation of the tank wouldn't result it high-speed debris striking Orion?

Offline robertross

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Might not the sudden, violent depressurisation of the tank wouldn't result it high-speed debris striking Orion?

Depressurization of the dome of the stage below?

Well first, the tank is at or near depletion, so whatever is left is low pressurant gas. Next, the domes are stronger than the walls, so the expansion would be outwards to the sides, not upwards. Yes, they will be seeing a thermal gradiant across the surface at ignition, but at that point it's also moving away from the tank. And there's a ton (for arguements sake) of service module between the dome and the heat shield, including bulkhead plates and tanks.

These are all well understood, and you can be sure the teams have designed around any chance of that kind of failure mode in the vehicle.   

Offline Lars_J

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Might not the sudden, violent depressurisation of the tank wouldn't result it high-speed debris striking Orion?

Depressurization of the dome of the stage below?

Well first, the tank is at or near depletion, so whatever is left is low pressurant gas.

How...? In most late ascent abort scenarios after LAS jettison, the upper stage will be completely FULL - where the SLS core has not been staged yet.

Offline robertross

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Might not the sudden, violent depressurisation of the tank wouldn't result it high-speed debris striking Orion?

Depressurization of the dome of the stage below?

Well first, the tank is at or near depletion, so whatever is left is low pressurant gas.

How...? In most late ascent abort scenarios after LAS jettison, the upper stage will be completely FULL - where the SLS core has not been staged yet.

Well in that scenario, the Orion is ABOVE the SM.
And in an abort, it would be moving away from the explosion.

I gave up on the math & physics (because I always got it wrong), but if someone wants to use the numbers:
SM ME: 27.7 kN  (+8 of 490N thruster, if they are part of the abort)

masses:
CM = approx 21650 lbs
SM = approx 27198 lbs

Also, the rocket engineers are the ones who are designing this, and you can be sure the astronaut office wouldn't put anyone in a vehicle that wasn't safe during an abort scenario (or it would defeat the purpose).

Offline Lars_J

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Orion is always above the SM, not sure what your point is.

I'm not suggesting that the people involved don't know what they are doing - I was merely pointing out that there will be a significant portion of the ascent between 1) LAS ejection and 2) SLS core stage burnout. In that time period, the SM abort engine would indeed be firing on top off a fully loaded iCPS(?) stage.

Or is it the plan to drag the Orion LAS almost all the way to orbit?
« Last Edit: 08/16/2014 07:44 pm by Lars_J »

Offline RonM

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Or is it the plan to drag the Orion LAS almost all the way to orbit?

The old Constellation plan had the Orion LAS jettisoned shortly after first and second stage separation. I'm assuming the same concept will apply to SLS. It's probably not needed in case of a problem with the second stage.

Offline Lars_J

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Ok, I stand corrected then. I had assumed that the core stage going almost to orbit meant that the Orion LAS would be dumped before it staged. Live and learn!

Offline Jim

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How...? In most late ascent abort scenarios after LAS jettison, the upper stage will be completely FULL - where the SLS core has not been staged yet.

And not an issue, just like it wasn't for Apollo

Offline Ronsmytheiii

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I'm not suggesting that the people involved don't know what they are doing - I was merely pointing out that there will be a significant portion of the ascent between 1) LAS ejection and 2) SLS core stage burnout. In that time period, the SM abort engine would indeed be firing on top off a fully loaded iCPS(?) stage.

Wont be a big deal, look at the 2:30 mark of this video showing a Titan II upper stage firing right at the first stage, it collapses but doesnt explode

« Last Edit: 08/16/2014 11:00 pm by Ronsmytheiii »

Offline Terran

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A little outdated, but I've not seen it here yet: Taken from ESA Bulletin May 2014:
Quote
Multi-Purpose Crew Vehicle European Service Module
(MPCV-ESM)
Recovery measures were implemented to get back on
track for FM1 shipment date of March 2017. The mass
non-compliance has been improved, and the remaining
over mass is considered manageable. Savings have been
identified with a new concept of a bellow water tank.
Deletion of a Command (and) Monitoring Unit should
allow a further saving. Clarification on Thermal Control
System mass increase and assessment of an alternative
radiator layout is under way. The MPCV mission data for
the ESM design and verification were baselined. The Crew
Module Adapter SM mechanical interface design was
agreed. The MPCV PDR is scheduled for 15 May with all
intermediate milestones achieved.

Some information and images about ESM in general can be read / viewed in an article about ATV. Page 32 of the bulleting. Including mission logo.

While the schedule for the ESM is tight and challenging, I think recent the concerns that the Service Module is the (main) cause of a schedule slip to 2018 for EM1 is just searching a scapegoat. Then again ESA would take the breathing room with open hands.
(Mentioned here: http://www.spacenews.com/article/features/41554news-from-aiaa-space-2014-nasa-officials-orion-%E2%80%98challenged%E2%80%99-to-make-2017)
« Last Edit: 08/18/2014 02:14 am by Terran »

Offline Proponent

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Wont be a big deal, look at the 2:30 mark of this video showing a Titan II upper stage firing right at the first stage, it collapses but doesnt explode

But the Titan II was unusual for a US rocket in that it used fire-in-the-hole staging, and was no doubt deliberately designed for such.  Most US upper stages separate and then ignite.  Unless there is firm information to the contrary, I would expect an Orion SM abort similarly to involve separation before ignition.

EDIT:  Added missing "abort".
« Last Edit: 08/18/2014 09:10 am by Proponent »

Offline Steven Pietrobon

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The old Constellation plan had the Orion LAS jettisoned shortly after first and second stage separation. I'm assuming the same concept will apply to SLS. It's probably not needed in case of a problem with the second stage.

The LAS is ejected at T+330s, during the core stage burn. From

S. Creech, J. Holladay and D. Jones, "SLS dual use upper stage (DUUS) opportunities," NASA, Apr. 2013.
http://ntrs.nasa.gov/search.jsp?R=20130013953
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline RonM

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The old Constellation plan had the Orion LAS jettisoned shortly after first and second stage separation. I'm assuming the same concept will apply to SLS. It's probably not needed in case of a problem with the second stage.

The LAS is ejected at T+330s, during the core stage burn. From

S. Creech, J. Holladay and D. Jones, "SLS dual use upper stage (DUUS) opportunities," NASA, Apr. 2013.
http://ntrs.nasa.gov/search.jsp?R=20130013953

Good find.

That's interesting, LAS is ejected before the core throttle down.

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