Particularly if you are trying the use the escape vehicle's engines as landing engines for the entire MCT. The forces on the connectors, which must be instantly separable during launch-abort, would be ridiculous.
Quote from: Paul451 on 10/07/2015 08:05 pmIt has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex. Yes. That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.;-)
It has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex.
Quote from: Lobo on 10/08/2015 11:13 pmQuote from: Paul451 on 10/07/2015 08:05 pmIt has to be a separate spacecraft, or it can't operate as a escape vehicle. Such a double-vehicle would become hideously complex. Yes. That's probably why such a cylinder-cone vehicle with a separable nose cone with a crew hab has never been thought of before.;-)Doesn't even need to be cylinder/cone:
[images of Apollo CM+SM and Dragon+trunk]
It's not really two spacecraft in one, like MCT+ S2 would be two completely separate spacecraft. It's more a spacecraft, with an additional section. Since everything below the lifeboat cannot function on it's own as it own spacecraft. So unlike your analogy, it's more like a semi tractor and trailer.
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.
I think the Separate Bi-conic is attractive in this regard because rocket stages are cheaper to develop per unit of dry weight then manned capsules
Quote from: Lobo on 10/09/2015 12:30 amBut the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated.Do you not understand that a vessel that must function independently and as a deeply integrated functional part of a larger vessel (your lifeboat) is going to be much more complex than a vessel that only has to function independently (a LEO taxi)? And that a larger vessel that must be designed around a major piece that separates is going to be much more complex than a similar sized vessel that doesn't come apart?
11. it needs to survive on Mars for about 550 days - longer if it does not return the next synod
My point is that MCT is already horrendously difficult to design, adding a lifeboat makes it far more difficult.
Those first ~3 MCT will serve as a monument for many generations of martians.
Quote11. it needs to survive on Mars for about 550 days - longer if it does not return the next synodThey can waive that requirement if they have to. I always anticipated that the first few MCT which have long surface times on Mars may never return. That would include the first passenger MCT that serves as habitat for at least one synod on Mars.Those first ~3 MCT will serve as a monument for many generations of martians. Later MCT will be unloaded, refuelled, checked then fly back to earth after a short stay. They will land on better prepared landing sites too.The really hard requirements are 5) 7) 9) 13) 14) But that is already plenty I agree.
Waive a requirement to last for 550 days on Mars, replace with requirement to last indefinitely ?!?!And the crew needs to get back somehow - first few missions won't have colonists.
Quote from: MikeAtkinson on 10/09/2015 08:01 amWaive a requirement to last for 550 days on Mars, replace with requirement to last indefinitely ?!?!And the crew needs to get back somehow - first few missions won't have colonists.Waive the requirement to fly back after that time. The ISS shows that a habitat can be maintained for decades. That would be more valid for a habitat that can at some point be connected to an external ECLSS specifically designed for Mars and an expanding local power supply.Part of the crew will go back with the passenger MCT that brings the crew that will man the station for the next synod and flies back after a few weeks. There will likely not be a life boat MCT. What would it be good for? It cannot go before the return window opens and that will be when the next MCT has arrived.
The Short-Stay Mission - often referred to as an opposition-class mission, this mission profile provides Mars stay times of 30 to 90 days with a round trip total time of 400 to 650 days. This mission class requires a large amount of energy to be expended in transit, even after taking advantage of either a Venus swingby (on either the inbound or outbound leg) or a deep space propulsive maneuver in order to limit Mars and Earth entry speeds.
So it is still a requirement to fly back one synod later. Not much of a gain there, at the cost of adding extra requirements about long duration surface stays and connection to external ECLSS.
Quote from: MikeAtkinson on 10/09/2015 10:00 amSo it is still a requirement to fly back one synod later. Not much of a gain there, at the cost of adding extra requirements about long duration surface stays and connection to external ECLSS.Sounds almost like you are deliberately misunderstanding me.
With you having been given advanced sight of the SpaceX MCT architecture, every word you post on this "speculation" thread from now onwards will be scrutinised with a fine tooth coombe until the grand reveal ! not that I'm suggesting in anyway that you should refrain from posting on this thread until the reveal, PLEASE keep on posting
As far as we know all MCT, both cargo and passenger, will go on trajectories that allow them to return after a short stay on Mars and return in the same synod. At least that is what Elon Musk has set as a goal for his transport system to reuse them every synod instead of every second synod.That means the return leg will be significantly longer than the leg earth-mars. You are introducing a new requirement for shorter return flights that would mean that manned MCT could not be reused every synod. That may or may not be the case. IMO it is just a reason to reduce the number of people who return to earth to a minimum, maybe have more water as shielding for at least a part of the crew space for the return leg. But that is problematic as the mass budget available for return is much smaller.
I think that's a good point about the difference between NASA Mars and SpaceX Mars. NASA Mars is very much focused on rotation. SpaceX Mars is to create a colony. I doubt they would be short of customers who would be willing to spend some cash (probably affordable to a lot of people via selling their home) and up sticks and become a resident of Mars.....and not return (the element of increasing the population, as opposed to several years stays and coming back).