Mars Colonial Transporter: What will it look like?

[Rakaydos]

The question is, then, can Raptor get a higher massfraction to orbit than Merlin?

[Nibb31]

It's Isp that matters. Raptor is a bigger engine, so it has more thrust, which means that you need less engines. It's supposed to use liquid methane, which is less dense, which means you need more tankage. Long duration cryo storage and transfer is another unproven technology that needs to be added to the list.

[Frozen_Heart]

12 minutes ago, Nibb31 said:

It's Isp that matters. Raptor is a bigger engine, so it has more thrust, which means that you need less engines. It's supposed to use liquid methane, which is less dense, which means you need more tankage. Long duration cryo storage and transfer is another unproven technology that needs to be added to the list.

Isn't ULA also working on that with their ACES upper stage? Heard they planned to do it by running an internal combustion engines with boiloff from LOX and LH, which then runs refrigeration equipment. Surely with something the mass of the MCT, the refrigeration equipment wouldn't be as much of a mass penalty compared to current rocket upper stages?

[CptRichardson]

4 hours ago, Nibb31 said:

It's Isp that matters. Raptor is a bigger engine, so it has more thrust, which means that you need less engines. It's supposed to use liquid methane, which is less dense, which means you need more tankage. Long duration cryo storage and transfer is another unproven technology that needs to be added to the list.

You presume that they will use liquid methane beyond Earth orbit. We don't yet know what their plans are for the Mars end of the trip, but it is ridiculously silly to assume they will do something like that.

[tater]

 

2 minutes ago, CptRichardson said:

You presume that they will use liquid methane beyond Earth orbit. We don't yet know what their plans are for the Mars end of the trip, but it is ridiculously silly to assume they will do something like that.

The whole point of methane in the first place was to create it at Mars using ISRU.

[magnemoe]

7 hours ago, Frozen_Heart said:

Isn't ULA also working on that with their ACES upper stage? Heard they planned to do it by running an internal combustion engines with boiloff from LOX and LH, which then runs refrigeration equipment. Surely with something the mass of the MCT, the refrigeration equipment wouldn't be as much of a mass penalty compared to current rocket upper stages?

ACES don't uses refrigeration as I know, or is it why they wanted a lot of heat from the engine? 
it use H2 and O2 as pressurization gas rather than helium, they also use h2 and o2 for trusters so they don't need monopropelant.  

With methane and oxygen you could probably manage without real refrigeration as long as you insulate the tanks well, run an helium cooling loop on the shadow side and use this for canceling out leaked heat. 

[Nibb31]

I have no doubt that it can't be done. It's just that it hasn't been developed or proven, along with the ISRU and refueling. There is a lot of engineering and testing to do before it can be used on a manned spacecraft. And SpaceX's "trial and error" development methods don't lend themselves well to the realities of the 2 year synod.

[Scotius]

3 hours ago, Nibb31 said:

I have no doubt that it can't be done. It's just that it hasn't been developed or proven, along with the ISRU and refueling. There is a lot of engineering and testing to do before it can be used on a manned spacecraft. And SpaceX's "trial and error" development methods don't lend themselves well to the realities of the 2 year synod.

Then who will do it? Space agencies seems to develop their systems at glacial speed. Maybe because they are under no pressure - "Meh, missions are planned for decades away. And by that time governments will change couple of times. Why bother?". Maybe private sector is what we need to break out of this circle?

[magnemoe]

3 hours ago, Scotius said:

Then who will do it? Space agencies seems to develop their systems at glacial speed. Maybe because they are under no pressure - "Meh, missions are planned for decades away. And by that time governments will change couple of times. Why bother?". Maybe private sector is what we need to break out of this circle?

As far as I know SpaceX has only used the trial and error part for the first stage recovery. Yes they have done lots of changes over the time but this is pretty common for aircraft too. 
The Kerbal way SpaceX did the Falcon9 first stage recovery development would probably not work well in an governmental organisation even if it was the cheapest and fastest way of doing this, the stages crashed after burnout so why not use them for testing recovery, just get data from the 10 first this is cheap, then try to land until you get it right. Now an governmental organisation tend to have low threshold for failures, at least very public ones and lots of fools see all the crashes as fails not as cheap tests. An dedicated program for recover stages with with an minimum of crashes would be far more expensive and slower. 
However this don't work for most stuff. 

 

[tater]

I posted this image in another thread or two...

This design is a Phil Bono design from 1963 (artist William Black: http://william-black.deviantart.com (his gallery is fantastic)):

450 mt to LEO. The diameter is 24m.

MCT is supposed to be lofted by BFR, and we guess MCT to be a nominal 150-180MT. Call it 150, and it's 1/3 of Rombus, and the volume of the BFR booster is roughly... 1/3 of Rombus.

Fascinating. 

[kerbiloid]

1 hour ago, tater said:

(artist William Black: http://william-black.deviantart.com (his gallery is fantastic)):

This gallery is amusing!

Also, Juvilado introduced another one:

 

[wumpus]

On 8/27/2016 at 2:42 PM, Nibb31 said:

It's Isp that matters. Raptor is a bigger engine, so it has more thrust, which means that you need less engines. It's supposed to use liquid methane, which is less dense, which means you need more tankage. Long duration cryo storage and transfer is another unproven technology that needs to be added to the list.

There's also the square/cube effect for air resistance.  A SaturnV-sized rocket will burn a smaller ratio of its fuel to over air resistance than a Falcon9 sized one.  But Isp is the big thing that matters.

[A Fuzzy Velociraptor]

7 hours ago, wumpus said:

There's also the square/cube effect for air resistance.  A SaturnV-sized rocket will burn a smaller ratio of its fuel to over air resistance than a Falcon9 sized one.  But Isp is the big thing that matters.

Air resistance is a very small portion of verlocity losses normally between 200-300m/s.

[Navy2k]

On 24.8.2016 at 8:12 PM, Scotius said:

I hope there will be voting process for the name of the first ship I bet top three proposals will be: Enterprise, Hermes and Ares

And the winner is: "Spacey McSpaceship"

[Rune]

On 25/8/2016 at 10:36 AM, Nibb31 said:

I think it will probably be two vehicles:

- BFR: A huge reusable first stage.

- BFS: An oversized Dragon. It will work as an upper-stage for getting to LEO, then it can be refueled by a couple of other BFS.

So basically, you need at least 2 BFS. One carries cargo to Mars. The other is used for refueling the first in LEO. You might need to wait for 2 or 3 refueling flights before you perform the Mars transfer burn.

You will need some sort of ISRU to get back, so the first cargo flight is going to need to carry an ISRU propellant plant.

Of course, this is a lot of technology to develop: HLV, ISRU, refueling, life support, interplanetary heavy propulsive landing, etc...  SpaceX can't realistically develop all of that in-house in less than a decade or two. 

Exactly my view of the matter.

The only thing I would amend is that if the rocket equation isn't failing me, and Raptor's Isp is 380s, then it would be more like 5 refueling flights for each outbound Mars trip.

They are gong to need the BFS to be somewhere around mass ratio ~4 when wet (~5km/s dV). If the BFR is just big enough to loft an empty BFS and its payload to LEO (on first analysis, somewhere around 200mT), then they would need around 600mT of propellant to launch the whole thing to Mars and land it there afterwards, meaning either six BFS with 100mT of propellants instead of payload, or a slighty more mass-efficient, purposely built thing that manages a better ratio. In any case, at the very least five BFR launches per Mars launch.

 

Rune. And that is why the BFR could make sense to reuse.

[Rune]

On 26/8/2016 at 2:48 PM, Nibb31 said:

One way to work out the minimum requirement for the BFS, you need to look for the dV requirements for each leg of the journey. Assuming it uses for the BFR and its own propellant load to get into LEO,  the other minimum requirements are:

LEO to Mars intercept and LMO to Earth intercept = 4260m/s

Mars surface to LMO =3800m/s

So assuming that the BFS is refueled in LEO and LMO by another BFS, and assuming it needs a few hundred m/s for propulsive landing and manoeuvering, the BFS needs to have at least 5000 m/s of dV with a payload of 80 metric tons.

In order to support 100 tons after landing, the dry mass of the vehicle will have to be at least 40 tons, including landing gear, structure, life support, heatshield, etc... (I think that's optimistic). So when you plug this data into the rocket equation with an average Isp of 320s, you get a total mass of 591 mt. Which is about the weight of a fully loaded A380.

To get the BFS to LEO; the BFR first stage is going to need to spend 4000 m/s and land. The Falcon 9 separates at Mach 10, which is 3430m/s, so it might be possible to push the envelope a bit more, but this means that the tanks of the BFS are empty when they reach orbit with its 80 ton payload. If you want to go anywhere, you need to fill it up. We've calculated that the BFS tanks are going to need to carry approximately 450 tons of propellant, and since the BFS has a 80 ton payload, you are going to need 6 BFS tanker flights to LEO and 6 to LMO to fill it up for each trip.

As for plugging the requirements of the BFR into the rocket equation, to get 4000m/s out of a 150-ton single stage with a 591-ton payload, you're rocket is going to weigh 2650 metric tons fully loaded. And that's without counting drag and gravity losses. Basically, that puts you in the Saturn V size category, with a BFR equivalent to the S-IC and S-II, and a BFS equivalent to the S-IVB and CSM/LM stack. The trick is in making the BFR and BFS reusable, which makes orbital refueling feasible.

Of course, to make this scheme work, SpaceX has yet to demonstrate:

• 1st stage reusability
• Powered landing from orbit
• Orbital spacecraft reusability
• Orbital refueling and propellant storage
• Fast turnaround of the above
• Long duration life support
• Mars reentry
• Mars powered landing
• Automated ISRU and ground refueling
• Mars launch
• Reentry from Mars

That really is an awful lot of technology to be developed by a single company.

Ok, I kept on reading, you did your math (and with more precision than I did!). Anyhow, if the Red Dragon mission architecture turns out to work, not only will SpaceX pretty much prove points #1, #2, #7 and #8 by then (assuming SES' launch proceeds some time next year), you can also dispense with all the LMO refueling flights.

Red Dragon will enter Mars straight from TMI, relaying on areodynamic forces to capture and slow down for terminal descent. I too didn't believe it would work even half as good as it apparently does, until I saw Scott flying a Dragon on realism overhaul, and he could control his descent rate with astonishing ease (I know lift is all about speed, but still, seeing the principle in motion to fly what is basically a brick in what is basically industrial vacuum, and control vertical speed to attain level flight at hyperbolic speeds is pretty rad).

Anyhow, after landing in a single stage from LEO, and given surface ISRU (which I concurr, won't be anywhere as simple as it sounds), then 5km/s are close enough to do straight shot home, I think, assuming just a slightly bigger mass ratio (5,5km/s per the wiki, I'm sure there are slightly lower energy trajectories, and MR4 is actually 5167m/s, 5,5km/s would be only MR~4.37). That simplifies the mission architecture, a lot. And the Falcon staging speed actually reinforces the idea of a beefy BFS with a high mass ratio.

 

Rune. Incidentally, MR5 and 380s gives you a beautiful 5999'66m/s. I'd totally set that as a design goal.

Edited September 7, 2016 by Rune

[wumpus]

On 8/26/2016 at 8:48 AM, Nibb31 said:

Of course, to make this scheme work, SpaceX has yet to demonstrate:

• 1st stage reusability -  They've certainly done the hard part, but it seems everything is delayed due to the explosion.
• Powered landing from orbit  - with a ~1k/2km/s "deorbit  burn" from Mars, it should be similar to a first stage on Earth.
• Orbital spacecraft reusability - I suppose they should start re-using Dragons.  Not sure if they are allowed in the contract.
• Orbital refueling and propellant storage - this sounds good, but I suspect that this will stay "dock with a fully fueled stage and jettison it when spent" for a long time.
• Fast turnaround of the above - unless you are out by the Moon, I suspect that "fast turnaround" could be multiple orbits without issue.
• Long duration life support - I suspect anyone supporting the ISS (i.e. the Dragon flights) has a pretty good understanding of this.  Radiation will be another story.
• Mars reentry - See "powered rentry from orbit"
• Mars powered landing - Again.
• Automated ISRU and ground refueling - This is quite possibly the only thing they have absolutely zero exposure to.  I can't imagine flying to Mars without a full return tank.
• Mars launch - Easier than Earth (although without much of the support).  Having all the fuel/oxidizer is the real kicker.
• Reentry from Mars - Again fuel storage.

That really is an awful lot of technology to be developed by a single company.

To me, it sounds like the really only "need" a few key technologies:

• zero boil-off systems.  If you can do liquid oxygen, liquid methane should be a piece of cake.  Hopefully they can hire (at least as consultants) the guys doing the James Webb telescope (liquid helium is wildly more difficult).  You aren't storing your fuel/oxidizer long term without them.
• ISRU - I'd avoid this if possible (yet the cost of *not* doing would likely end the mission unless cheaper propulsion is possible).
• ion propulsion* (does not appear to be part of the Musk plan, but should make things wildly easier).  Bring your cargo to Mars on the cheap (and slow).  At least 60% of the mass in the NASA plan is in unmanned rockets.  And of course the mass of the manned rockets is almost entirely fuel which need not be transported by chemical means either (dock with a "fuel tank" (read fully gassed up stage) in an elliptical orbit (for pe-kicking around Earth).  Why are you using an Isp of <400 when >4000 is available for 90% of your mass*delta-v?

Much of the other tech are small steps (although Elon Musk has shown a love for even smaller steps whenever possible) from existing tech (and too many small steps at once add up to impossible risk).  And a lot of this will be reduced (i.e. many of the small steps proven) by sending an unmanned dragon to Mars.  I remain convinced that ion propulsion (of anything that doesn't have to be manned) is the way to Mars.  This includes as much fuel as possible: using such thrusters to get it to high orbit (and looping around the Moon if necessary, your thrusters want to move in circular orbits and you want any fuel stages to end up in highly elliptical orbits).  There remains the problem of avoiding the Van Allen Belts, but that should be possible to plot a course similar to the Apollo missions to avoid them.

I'm not at all convinced that upper stages need be reused.  Unless they can somehow contain the overall cost of launching a rockets, the costs of the falcon are mostly the booster, followed by launch/logistics cost, followed by upper stage costs.  Spending so much time on the vastly harder scheme of re-using an upper stage does not appear to be productive.  Reduction of launch costs *should* be wildly easier (see DC-X for examples).

And then there's the ISRU.  My guess is the first unmanned trip to Mars needs to bring one along, and it has to work if spacex wants to go to Mars.  Even with a working ISRU, it will be a huge challenge for the astronauts on Mars to refuel and launch the thing with Houston so far away.  Or you could deliver all the fuel you need [very slowly] with ion propulsion and gravity assists.

* note that ion propulsion might not be the ideal high Isp means of propulsion.  It simply is the one proven via NASA (and other space programs) flight.  Also don't be surprised if the Isp goes way down if you have to substitute Ar for Xe due to the impossible masses of Xe required (Ar is more common than CO2, Xe is *rare*).  In case you hadn't noticed, that Isp in KSP are pretty close to the real thing, but the thrust is even worse (they would be a lot more popular if you could use them while time accelerating.  Since IRL you can't time accelerate anyway, the low thrust is more of an issue with plotting a course and capture (you can't just Hohmann over and burn to capture).

[Rakaydos]

So there's some indications that Ron Howard's Mars MAY include spoilers for Elons big mars plans

 

http://www.popsci.com/watch-trailer-for-ron-howards-mars

[kerbiloid]

6 minutes ago, Rakaydos said:

So there's some indications that Ron Howard's Mars MAY include spoilers for Elons big mars plans

They plan to use a changed Terminator main theme as a musical background.

[DerekL1963]

2 hours ago, wumpus said:

To me, it sounds like the really only "need" a few key technologies:

That's mostly because you've handwaved away all the problems Nibb31 pointed out.

To take just one example of your ludicrous handwaving:   "Long duration life support - I suspect anyone supporting the ISS (i.e. the Dragon flights) has a pretty good understanding of this."  Huh?  They didn't design the ECLSS, didn't build the ECLSS (they didn't even exist when it was built), and don't operate the ECLSS.   Their only connection to the ECLSS is that of being a FedEx driver.   They have precisely zero experience with long duration ECLSS.  Heck, their flight experience with any duration of life support is essentially zero.

 

2 hours ago, wumpus said:

ion propulsion* (does not appear to be part of the Musk plan, but should make things wildly easier).  Bring your cargo to Mars on the cheap (and slow).  At least 60% of the mass in the NASA plan is in unmanned rockets.  And of course the mass of the manned rockets is almost entirely fuel which need not be transported by chemical means either (dock with a "fuel tank" (read fully gassed up stage) in an elliptical orbit (for pe-kicking around Earth).  Why are you using an Isp of <400 when >4000 is available for 90% of your mass*delta-v?

Why?  Because the ion engines and the requisite power supplies sufficient for cargo of any significant quantity (heck, any quantity over thirty or forty pounds) simply doesn't exist.

[Mitchz95]

What day is Musk doing his talk at the IAC? (assuming it's not postponed after Amos-6)

And will there be a livestream?

Edited September 16, 2016 by Mitchz95

[Spaceception]

Obviously he means human wise, but that's cool.

 

Edited September 17, 2016 by Spaceception

[RedKraken]

Some more issues raised in the NASA forums :

1. Angled engines for landing and take off on Mars : 

   Dont want debris (small rocks and dust) shredding the engines or damaging the ship.

   The engine dugouts in the heatshield may turn into trenches so the engines can be angled out when required.

2. Vacuum raptors may not be ideal for final touchdown on mars (300% too big ) and will not perform well for an atmospheric earth landing.

    So we might get a group of smaller (750kN?) dual-purpose (atmos/vac) landing engines at the expense of payload.

3. Refueling in LEO : 

   Mass fraction for two-stage BFR/MCT fueler is horrible.

   A three-stage vehicle will double your mass fraction and halve your refueling launches.

   You could recover your second stage on a ballistic trajectory.

Edited September 17, 2016 by RedKraken

[Mitchz95]

According to Elon on Twitter, it's now called the ITS: Interplanetary Transport System.

[Spaceception]

On 9/16/2016 at 10:31 AM, Mitchz95 said:

What day is Musk doing his talk at the IAC? (assuming it's not postponed after Amos-6)

And will there be a livestream?

2nd day, 1:30 to 2:30 pm.

Dunno, hopefully.

6 hours ago, Mitchz95 said:

According to Elon on Twitter, it's now called the ITS: Interplanetary Transport System.

SPACESHIP!!!

6 hours ago, Mitchz95 said:

According to Elon on Twitter, it's now called the ITS: Interplanetary Transport System.

SPACESHIP!!!