Quote from: Hauerg on 11/09/2020 05:22 pmSuch a sad mission architecture.I basically agree with this assessment. The architecture is built around a [1] subservience to the rocket equation, and the notion that propulsion gets prohibitively expensive the "further out" you use it. (In this case the returning Orion is so "far" from its launch site that it has essentially zero propulsion budget remaining [2] and relies on atmospheric braking [3] to slow down.)As many have opined, the solution to breaking the tyranny [4] of the rocket equation is to produce propellant somewhere along the way. And the surface of Mars sure seems like a great place to do that!
Such a sad mission architecture.
Quote from: ncb1397 on 01/25/2021 04:40 pmQuote from: Coastal Ron on 01/25/2021 03:02 pmThe simple reason is that the current Orion MPCV design is oriented towards supporting missions to our Moon, with up to 21 days of active crew time plus 6 months quiescent spacecraft life. A Mars mission would last at least two years.That is largely a limit on the service module O2 supply...Adding more O2 is potentially a relatively trivial matter. Replacing the 275 bar tanks with 800 bar tanks (equivalent to consumer available hydrogen fuel cell vehicle tanks) would increase O2 supply by a factor of 2.9 increasing crew air to ~61 days while not increasing footprint.OK, now the crew in the cramped capsule can survive 61 days of a 780 day trip. I'm not sure you're solving the basic problem here - there is no use for an Orion spacecraft on a Mars journey until you get really close to Earth, in which case you've been hauling this massive weight around the solar system for little ROI.The "Orion MPCV" as currently designed is for traveling to the Moon. Period. If the want to scavenge the Orion MPCV design for usable parts for a Mars vehicle, great, but it won't be called the "Orion MPCV" anymore, will it?Plus, why keep trying to put lipstick on this pig. For the same amount of effort you can likely just design a new space-only fully-reusable spacecraft that can be used to go to Mars.
Quote from: Coastal Ron on 01/25/2021 03:02 pmThe simple reason is that the current Orion MPCV design is oriented towards supporting missions to our Moon, with up to 21 days of active crew time plus 6 months quiescent spacecraft life. A Mars mission would last at least two years.That is largely a limit on the service module O2 supply...Adding more O2 is potentially a relatively trivial matter. Replacing the 275 bar tanks with 800 bar tanks (equivalent to consumer available hydrogen fuel cell vehicle tanks) would increase O2 supply by a factor of 2.9 increasing crew air to ~61 days while not increasing footprint.
The simple reason is that the current Orion MPCV design is oriented towards supporting missions to our Moon, with up to 21 days of active crew time plus 6 months quiescent spacecraft life. A Mars mission would last at least two years.
Wrong, Wrong, Wrong!!!. Why do people keep posting this?The designs/CONOPs/DRMs for the CEV/MPCV were never to house crew for the cruise to and from Mars. It was never the intent.Its job is to launch crew to the MTV, fly with the MTV as a backup control center and as a safe haven and to return the crew to earth from the distance of the moon upon returning from Mars.
So, here is my operational concept for an Orion flight to mars orbit and back. -two launches of SLS Block 1B/2 vehicles. Block 1B gets between 31.6 t and 34.3 t to the Mars C3 of ~10 km^2/sec^2.-each SLS launch carries an Orion crew capsule with 2 crew each. The two orions will dock during trans-mars transits. They may or may not undock during mars orbit insertion and mars departure burns. They of course undock prior to earth re-entry.-departure is Nov-29-2028, earth return is Sep-19-2031, duration is 1025 days. -Orion gas delivery system contains 4 O2 tanks rather than 2/3 O2 tanks and 1/2 N2 tanks.-O2 tanks are 550 bar(double baseline) holding 66 kg of O2 each or 264 kg.-280 kg of water is stored in the ESM (baseline capacity)-an additional 2.7 t(2.7 cubic meter) water tank is constructed in each Orion (see diagrams for rough geometry. -In addition, a urine processor, solid oxide electrolyzer unit similar to Mars 2020 Moxie (but an order of magnitude higher capacity), water electrolyzer and improved bathroom/waste management system is installed in each Orion replacing where two of the seats would be in the baseline Orion-Mars insertion delta-v is 854 m/s, Mars departure delta-v is 519 m/s, total delta-v required to be provided by Orions is 1.37 km/s.O2 requirements are 1024 days * 4 astronauts * .84 kg/day = 3.44 t -each Orion carries .264 t in the ESM gas delivery system (.528 t total) -each Orion carries 2.98 t of water (5.96 t total). ~89% of the water content is O2 or 5.3 t. Water is recycled through the urine processor and then electrolyzed. Hydrogen is vented. -The solid oxide electrolyzer recovers half of O2 content in CO2 as recycled O2, giving margin.water requirements are 1024 days * 4 astronauts * 1.5 kg or 1.5 liters/day = 6.144 t -each Orion carries 2.98 t of water in integral containers(5.96 t total). -an additional 184 kg is carried as logistics in Orion logistics boxes.food requirements 1024 days * 4 astronauts * 1 kg/day = 4.096 t -each Orion carries ~2 t eachBaseline Orion masses: 25,848 kg + 132 kg gas due to higher capacity tanks + 100 kg gas tank mass + 2700 kg in water in water tanks + 300 kg internal water tank dry mass and support structure + 170 kg SOXE (10x Moxie) + 400 kg electrolyzer - 50 kg reduced seat mass +400 kg improved bathroom +2000 kg dehydrated foodMass estimate: 32 t compared to a Block 1B estimated capacity of 31.6 - 34 t (c3=10 km^2/sec^2, slightly higher than baseline trajectory of 8.2 km^2/sec^2) and Block 2 estimate of 37.6 t. Orion Total delta-v capability: 316*9.8*ln(32,000 kg/23,400 kg) = 969 m/s. There is a 400 m/s delta-v shortfall with the existing Orion propellant tanks because of the added mass (Orion without the upgrades would be a lot closer). Pretty amazing how close it is to closing though. A few possible solutions...-Space station in mars orbit pre-stocked with supplies and/or fuel-reduction of logistics (but how?)-increased fuel in ESM (this almost definately pushes it into the Block 2 category).-dump waste before mars orbit insertion/trans earth injection-account for gas venting/dumps.edit: So, fixing a few issues with the architecture. The service module needs stretched propellant tanks by about 2.5 feet to carry an extra 3-4 t of propellant. Logistics (water, food, etc.) gets moved to a USA carried logistics module with 2 Orion compatible docking ports. This module needs to mass under 2 t. One of these is ejected prior to mars orbit insertion, the other one is ejected prior to trans earth injection. This allows for trash disposal every 1 year and moves most of the water, food, etc. out of Orion on launch. Total mass to trans mars injection ends up at 37-38 t (Block 2 territory). Block 2 might need to be sized slightly bigger to fit this mission. So, to wrap up...Crew Module - heat shield upgrade, improved bathroom module, improved ECLSSService Module - higher pressure O2 tanks, stretched propellant tanks.-Orion Cargo Module (OCM) - this is new, ~3 meter diameter and 3 meter length, must mass under 2000 kg. Could be Cygnus derived.
I don't think Orion is going to Mars by itself. NASA would probably use a mother ship for it to dock with, then have a Mars lander also docked with the mother ship. I think Orion was only designed to get to the moon and dock with a moon lander or a moon station like Artemis station.
Quote from: spacenut on 06/29/2021 01:25 amI don't think Orion is going to Mars by itself. NASA would probably use a mother ship for it to dock with, then have a Mars lander also docked with the mother ship. I think Orion was only designed to get to the moon and dock with a moon lander or a moon station like Artemis station. There's no "think" or "probably" about it. Orion's role in a Mars mission was *always* to dock with a Mars Transfer Vehicle at the start of the mission, and to undock and return the crew to Earth at the end. Every single NASA DRM since the ESAS report has been based on that. Just like Jim and woods170 have already said.This is not the first thread on this forum to propose this strawman about Orion going to Mars by itself. It's absolute nonsense and it needs to stop.
...I mean, go over to SS threads. Apparently it will replace all commercial aviation and all launch vehicles and not a single eye has been batted
As far as the pure O2 environment, every successful manned BEO flight has used a pure O2 environment post launch. I don't see an issue with it. Just transition to pure O2 low pressure post launch and things should be fine.
Any unbiased review of the capabilities of the Orion shows that it is only usable in Earth-local space. Hauling it to Mars makes no sense, and the Orion is easily replaced by a fully reusable space-only transportation system, which we need anyways if we want to expand humanity out into space.Quote from: Khadgars on 06/29/2021 01:42 am...I mean, go over to SS threads. Apparently it will replace all commercial aviation and all launch vehicles and not a single eye has been batted Go to any major NSF topic and there are threads with edge-case topics, like this one. Just because most of us ignore them doesn't mean we endorse them...
Quote from: ncb1397 on 06/29/2021 02:37 amAs far as the pure O2 environment, every successful manned BEO flight has used a pure O2 environment post launch. I don't see an issue with it. Just transition to pure O2 low pressure post launch and things should be fine.Every flight of more than two weeks' duration has used a mix-gas atmosphere, because of pure oxygen's toxicity.
(I think by the time anything like this comes to fruition, the astronauts will be using oversized iPads with WiFi or other wireless connectivity, and will do most of the system control and monitoring from wherever they happen to be. In the first Star Trek movie, they seem to have invented the Kindle, but the writers didn't realize they could download ALL the engineering documents and designs and schematics into one device, so they had separate tablets for each document. They would hand them off to each other when someone needed the docs for the life support systems or long range scanners.)
Quote from: Proponent on 06/29/2021 12:35 pmEvery flight of more than two weeks' duration has used a mix-gas atmosphere, because of pure oxygen's toxicity.So, would skylab's mixture of 26% nitrogen at 5 psi work? Or because this was only done for up to ~3 months, there is still a problem for longer duration missions?
Every flight of more than two weeks' duration has used a mix-gas atmosphere, because of pure oxygen's toxicity.
That would still allow for a lighter cargo module. You would still have to carry nitrogen or some other inert gas, but not as much. It is still highly debateable what the long term effects of low pressure oxygen is. There was basically no discernable effects at 2 weeks. If I wasn't clear, this would be a low pressure environment and so typical oxygen toxicity at elevated partial pressures shouldn't really apply. But do you have a study suggesting long term exposure past 2 weeks is a problem, or is it just a question mark that we can't rule out at this point?
