ITS ship variants

[mikelepage]

I'm hesitant to add yet another ITS-themed thread to the forum, but it seems to me that many of the ITS threads being added in the last few days are basically rehashing the issues with human space flight, this time as it applies to the shiny new rocket on the block.  This thread hopefully amalgamates some of those threads.

IMO The greatest aspect of what SpaceX has achieved with the ITS is to clearly define a set of standards which are plausible for the near future of human space flight in the inner solar system.  The choice of Methane/Oxygen is meaningful because it can be generated from CO₂/Water/solar electricity which is available at most destinations we might foreseeably travel to.  It makes sense that there would be a standard propellant/oxidiser combination used across all human spaceflight, and better to stick to that standard from the beginning.

Although the ITS ship design itself is pretty vague, its size/mass is determined by how big it needs to be to land a "substantial" payload on Mars, yet still be able to achieve Mars escape velocity, transit back to Earth, and land.  The size/payload capacity of the ITS booster is as big as it needs to be to put such a ship into LEO. 

This is great because now we have some more solid numbers to work with, and a common theme amongst many of the threads is that people are imagining different variants on the ITS ship as required to solve whichever problem they find most interesting.

What I find interesting is having this booster/ship architecture makes it possible to address many of those requirements, so this thread is about trying to figure out how many variants of the ITS ship there need to be.  If you keep the Methane/Oxygen tanks core architecture constant, but everything else is interchangeable, what other potential uses can we come up with?

So far we have two variants:
1) ITS ship crewed
2) ITS ship tanker (Methane + LOX).

But I could imagine a large number of variants appearing with time.  So perhaps a future lineup would look like this:

1) ITS ship crewed:
a) atmospheric lander
b) vacuum lander for planetary mass moon/asteroid missions (Luna, Ceres, Ganymede etc)
c) vacuum space station/orbiter for long duration missions to lower mass asteroids/moons or LEO - perhaps it deploys into larger radius structure for spin gravity?

2) ITS tanker:
a) Methane + LOX
b) H₂O

3) ITS Cargo: large cargo bay doors/cranes to transport large equipment to and from destination. 

4) ITS ISRU/power/habitat transport modules designed to stay at destination and be crewed/function once arrived - can be remotely deployed and/or flown in suborbital hops to be better positioned for resource requirements on site.  Probably all three functions would be combined at first, then separated in future.
a) In situ resource utilisation (ISRU) factory
b) solar/(nuclear?) power station,
c) Large habitat/greenhouse - after landing it becomes the center point for an inflatable dome structure.

5)?

Initially maybe only 1 in 4 ITS ships to Mars are actually crewed (early missions would likely have extra type 4 ITS ships meant to stay and perform specific functions: ISRU/power/habitat/greenhouses etc).  These uncrewed cargo ships land in the days before the crewed ship arrives, and astronauts use telepresence to pilot the cargo ships in short hops so they are close to each other and desirable resources.  Then the crewed ITS can come down close and hop into final position.   As the colony became more self sufficient you would have less type 4 ships and more type 2/3 ships.

Thoughts?

[hkultala]

It seems that the most favourite ones in this forum are earth-SSTO models where all vacuum engines are replaced with sea level ones.

(so may threads are full of ITS earth SSTO speculation)

[Ludus]

I think ITS Cargo is the most glaring omission. EM has said that Mars would require about a 10:1 ratio of cargo to passengers and this would imply that most of the fleet each synod would be cargo only. I'd take cargo variants to look about like tankers but be configured about the same as passenger versions for tanks, with big cargo doors on the front section which is just a big payload bay.

This variant also happens to be essentially a big unmanned shuttle replacement that can lift things very cheaply into earth orbit. It's the variant that would be used for unmanned missions to ice moons or other exploration.

This seems to imply that SpaceX would mostly be building this cargo spaceship and comparatively small numbers of the big booster, tankers and manned variants. A few boosters and tankers could support a lot of them since they have rapid reuse cycles.

[go4mars]

There's also the "powered clamshell" talk from a few years ago.
Perhaps that simplifies pad logistics/timeline for satellite prep.

To the satellite prep people - could that be so?

[Blackjax]

There's also the "powered clamshell" talk from a few years ago.
Perhaps that simplifies pad logistics/timeline for satellite prep.

To the satellite prep people - could that be so?

I've been increasingly wondering if a vehicle for delivering payloads to orbit will be the 'other' variant.  We know they want full reusability, what if this is how they crack the nut of dealing with the fact that the second stage and fairing on the Falcon family are not reusable and might be problematic to ever make reusable.  If you have a fleet of booster stages designed for heavy reuse that are pretty inexpensive to launch relative to today's expendables and aren't always needed for mars payloads, why wouldn't you make a completely reusable second stage that can deliver a satellite to a given orbit then RTLS?  Sure it is super oversized for current satellites, but how does that actually matter if the all in cost to get those payloads where they need to be is a fraction of the costs of what the much smaller launchers can do it for today?  Using the ITS for this basically subsidizes a lot of the Mars infrastructure.  If it lets you retire the Falcon line and switch to optimizing everything you do from manufacturing to operations around a single set of technologies and hardware, even better.

What if the Falcon line only lasts until this next generation proves itself?

[dror]

1- LAS -
The crew section will be completely seperated from the cargo bay and will have its own pusher engines.
Some of the fuel which is needed for landing will be stored in the crew section.

2- cargo-
The crew section is missing in this configuration, which is similar to a normal seconed stage with or without a faring. This will allow the launch of very big fairing-incorporated modules which will serve as a permanent space station or a pre-fitted orbital factory.

3- SFR-
A much smaller version of the system, 3-5 times smaller, to fill the huge gap between mars needs and LEO needs. This version will carry 20-40 passangers to the commercial space stations and or 50-100 ton, fully reusable.
It will be sized to refuel with a single ITS tanker to allow the same capacity to the Moon or Mars.

[DOCinCT]

I think ITS Cargo is the most glaring omission. EM has said that Mars would require about a 10:1 ratio of cargo to passengers and this would imply that most of the fleet each synod would be cargo only. ...I'd take cargo variants to look about like tankers but be configured about the same as passenger versions for tanks, with big cargo doors on the front section which is just a big payload bay.

I'm not sure it's an omission as much as just not talked about in detail.  All that has been shown so far is a drawing of a passenger version.  While mentioned, the tanker version has no illustration of how it would be configured.  Elon did say, elsewhere, that a cargo version would be the first spaceship to Mars.

[Long EZ]

Once a cargo ITS is landed on Mars, offload the cargo, then lay the ITS down sideways and put it into a trench. Then cover it with regolith. Then use the methane and LOX tanks as hab/farm space. Being sideways would give a large area for growing crops or living space. Also it would ease access to and from the surface. Basically, pre-outfit the tanks with floors and racks as needed for the intended use.

I also like the idea of the cargo ITS having a small crew compartment at the nose.
If a tanker ITS had a small crew compartment in the nose it would make a great craft for early lunar flights.

[moralec]

The choice of Methane/Oxygen is meaningful because it can be generated from CO₂/Water/solar electricity which is available at most destinations we might foreseeably travel to.

Maybe a variant could be a full size, self sufficient Methane and LOX generation facility. A ship that could travel to mars with the rest of the fleet, and start producing propellants almost immediately after arriving.

[AncientU]

The choice of Methane/Oxygen is meaningful because it can be generated from CO₂/Water/solar electricity which is available at most destinations we might foreseeably travel to.

Maybe a variant could be a full size, self sufficient Methane and LOX generation facility. A ship that could travel to mars with the rest of the fleet, and start producing propellants almost immediately after arriving.

I really like this idea. 

When the entire Propellant ISRU Facility is pre-packaged -- including existing or even over-sized tankage, which will also need some thermal isolation to avoid the CO₂ freezing out on its walls -- it can be deployed where needed to jump start fuel processing.  Could carry water seeking/harvesting vehicle(s) as well as fuel transfer 'trucks'.  Once an outpost is established and has surface facilities at a significantly larger scale established, the craft can be relocated where needed for another start-up.

A similar facility in a can could be used for a nuclear electric/thermal plant or other large, essential infrastructure components needed to get surface exploration outposts/settlements started. 

These vehicles would go to Mars and never return.

[hallmh]

I think a subcategory of the Tanker variant would be an orbital tank farm segment.

It seems likely, and has been discussed here, that the ships on their way to Mars or elsewhere won't want to hang around while five tanker flights shuttle up and down to bring them the fuel for their onward journey. It would be simpler, and safer, to have a fuel supply prepositioned in orbit.

One way to do it would be to launch the fuel supply in the form of a bunch of uncrewed tankers, in the days before a mission. But that would be a very wasteful approach, as you're sending up a lot of mass (descent engines and structure) that could be additional fuel; and you'd need to make five times as many tanker vessels.

I can imagine an ITS variant that is stripped down entirely, with nothing inside except a tank designed for long-term storage of either LO2 or methane, plus the necessary refrigeration plant. This would be launched with the tank containing enough of its intended contents to make up a full launch load.

If they were shaped as a pentagonal prismpyramid, 12 of these tanks would fit together to make a dodecahedral structure that would minimise the surface to volume ratio.

[DOCinCT]

Once a cargo ITS is landed on Mars, offload the cargo, then lay the ITS down sideways and put it into a trench. Then cover it with regolith. Then use the methane and LOX tanks as hab/farm space. Being sideways would give a large area for growing crops or living space. Also it would ease access to and from the surface. Basically, pre-outfit the tanks with floors and racks as needed for the intended use.

I also like the idea of the cargo ITS having a small crew compartment at the nose.
If a tanker ITS had a small crew compartment in the nose it would make a great craft for early lunar flights.

I don't think that is practical, at least for the crew/cargo sections.  A tire lying flat on the ground has a fair amount of horizontal surface area BUT if you stand it on end, you just have a small section at the bottom before the "walls" curve upward. 

[CuddlyRocket]

Once a cargo ITS is landed on Mars, offload the cargo, then lay the ITS down sideways and put it into a trench.

I don't think you can hand-wave away that little maneuver! How do you propose to accomplish it?

[mikelepage]

The choice of Methane/Oxygen is meaningful because it can be generated from CO₂/Water/solar electricity which is available at most destinations we might foreseeably travel to.

Maybe a variant could be a full size, self sufficient Methane and LOX generation facility. A ship that could travel to mars with the rest of the fleet, and start producing propellants almost immediately after arriving.

I really like this idea. 

When the entire Propellant ISRU Facility is pre-packaged -- including existing or even over-sized tankage, which will also need some thermal isolation to avoid the CO₂ freezing out on its walls -- it can be deployed where needed to jump start fuel processing.  Could carry water seeking/harvesting vehicle(s) as well as fuel transfer 'trucks'.  Once an outpost is established and has surface facilities at a significantly larger scale established, the craft can be relocated where needed for another start-up.

A similar facility in a can could be used for a nuclear electric/thermal plant or other large, essential infrastructure components needed to get surface exploration outposts/settlements started. 

These vehicles would go to Mars and never return.

In many ways it makes sense to have ISRU capability built into an remotely controllable vehicle (an ISRUV), so it could make suborbital hops as required to seek pure water ice for ISRU.

1) It makes more sense (early on when energy is at a premium) for the ISRUV to use pure water ice rather than trying to extract it from 5-10% water in regolith.  This likely means going to glaciers (it turns out there are non-polar glaciers: http://astronomy.com/news/2015/04/mars-has-belts-of-glaciers-consisting-of-frozen-water).
2) A colony will be close to the equator for PV/greenhouse requirements - but since you don't necessarily want to build your colony on a glacier, it would help to be able to separate the two sites.
3) Therefore you want a craft that can hop to glaciers wherever they are, use ISRU to fill up its tanks with methane/LOX/water ice and hop back to the vicinity of the colony to a) refuel the ITS crew ship and b) provide the colony with large amounts of relatively pure water ice.

Low Mars orbit is a dV of 4.1km/s and the total capability of the ITS ship is just barely SSTO on Earth (8km/s) so these definitely have to be suborbital hops. 

Initial hops can be small (maybe a few km cross range), but I wondered, "how big can these hops be?" So I've tried to do some calculations for suborbital PTP on Mars:



The dry mass of ITS is 150 ton and let's assume 100 ton of ISRU machinery built into the ship.  Also the tanker version has 2500 ton of propellent, so I'm assuming a total mass of 2650 tons.

Imagining we have a cycle where the ISRUV is going from glacier to colony and back.  No special software here: (just http://www.strout.net/info/science/delta-v/) and modelling the rocket as a simple ballistic projectile.

Flight 1 (ISRUV lands directly on glacier during entry and commences ISRU).  Once full:
Starting mass: 2650 t
Final mass: 1250 t
Isp: 382
dV: 2815 m/s

Flight 2 (from colony back to glacier)
Starting mass: 550 t
Final mass: 250 t
Isp: 382
dV: 2954 m/s

It does seem to me that allowing a suborbital hop with launch/landing burn dVs of ~1.3km/s (with reserves) and a cross range of ~700km is possible whilst still delivering 700 ton of propellent and water per cycle.  The crew vehicle needs 1950 ton of propellent to return to Earth, so 3 cycles gives you the necessary ISRU-derived propellent delivery plus 150 ton of glacier water ice.

The other part of this is that obviously you don't want anyone in the crew vehicle when the ISRUV is coming in to land close by.  Therefore you need a 4th ISRU ship variant which lands ahead of time, which I'm imagining as a dedicated hab variant - big inflatable dome that unfolds something like a lotus flower with thin film solar cells over a greenhouse etc.  The colonists spend most time there, a safe distance away from the ITS crew ship.

I think it follows that 700km is also near the maximum distance two colonies should be from each other for safety/bailout purposes.