Author Topic: ITS Ships Flying As a Group  (Read 4058 times)

Online sanman

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ITS Ships Flying As a Group
« on: 06/20/2017 01:46 PM »
Suppose that once the ITS ball gets rolling, and there are multiple ships departing for Mars simultaneously (eg. >5) -  then does it make sense to have specialization in roles among these ships? Should each ship be a jack-of-all-trades, or should particular ships be tailored for better capabilities in certain respects?

Should ships fly in a formation? Could they even fly while being physically linked/clustered together, for added radiation shielding during the voyage? What are the pro's and cons of this?

In a pod of whales, or a flock of geese, or an aerobatics team, one takes the lead and the others all follow the leader.
Is there any inherent survival advantage of doing this for a Mars trip?

If ships were physically docked together, to allow passage between them, then perhaps it could allow a wider sharing of space and pooling of resources among them - but that also might create a greater collective risk exposure among them. What are the pro's and cons?

I was thinking that rather than each ship having its own full-fledged eatery, there could be one ship in the cluster which would be the "cafeteria ship" where everybody could go to eat, in staggered shifts, like on cruise ships.
As a local backup, each ship would have its own little stockpile of rations, in case access to cafeteria ship was no longer available.
Likewise, one ship could be the "infirmary ship", and would be better equipped for medical issues.
Etc, etc.

If any particularly hazardous cargo was being transported, perhaps that ship would be kept separate from the cluster, in order to avoid posing risk to the others.

What are the advantages and drawbacks of the specialized approach vs the generalized approach?
What are the advantages/disadvantages of flying linked, as opposed to flying separately?
« Last Edit: 06/20/2017 03:25 PM by sanman »

Online guckyfan

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Re: ITS Ships Flying As a Group
« Reply #1 on: 06/20/2017 03:26 PM »
I am assuming that this would be an expedition beyond Mars, on a multi year flight. While I argue against AG on flights to Mars, for a mission that may take 20 years AG will be needed IMO. It will also be a major endeavor which will need a lot of money. I envision it like this:

At least 8 ships will launch into their trajectory. 6 ships will be docked in a ring once on their way with passage tunnels to link them. That would provide a structure of more than 25m. Enough to provide near Mars gravity without major issues. At least 2 ships are spares to fill in gaps if a ship fails and needs to be left behind. Major maneuvers will require undocking and redocking after course correction. Minor course corrections can likely be done while connected, maybe even without unspinning them.

Each function needs to be available on two ships so one can be abandoned if necessary. Nuclear power plants with enough capacity to produce propellant on any site that has water and CO or CO2. Should be available in the outer asteroid belt and the outer moons of Jupiter or Saturn.

Hydroponics to produce fresh vegetables. Maybe not enough as a biologic ECLSS. Crew size, I think not less than 12 or 15.

Offline RonM

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Re: ITS Ships Flying As a Group
« Reply #2 on: 06/20/2017 03:48 PM »
With the massive amount of exhaust from multiple Raptor engines, can several ITS spacecraft safely leave orbit simultaneously without damaging each other?

Offline spacenut

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Re: ITS Ships Flying As a Group
« Reply #3 on: 06/20/2017 03:58 PM »
Maybe if they are on slightly different planes to be able to run parallel, allowing one to dock with another in case of emergency. 

I do like the idea of connecting several together with side docking.  Then attach some type of reinforcing so all can fly connected and slightly spin to create artificial gravity.  Separate when at Mars for individual landings.  No worries with zero-g.  This would allow for trips longer than the synod Musk suggests for Mars travel.  So ITS could fly this way even during off synod for continuous Mars operations. 

Online flyright

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Re: ITS Ships Flying As a Group
« Reply #4 on: 06/20/2017 04:08 PM »
I think the problem with docking ships together was figuring out what to do with all the solar arrays so they don't overlap each other. This issue was discussed previously, but I haven't found the thread yet.

I do think formation flying should be possible. They would need to do Mars injection burns at close intervals, but not necessarily at the same time.


Online guckyfan

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Re: ITS Ships Flying As a Group
« Reply #5 on: 06/20/2017 06:01 PM »
I think the problem with docking ships together was figuring out what to do with all the solar arrays so they don't overlap each other. This issue was discussed previously, but I haven't found the thread yet.

I do think formation flying should be possible. They would need to do Mars injection burns at close intervals, but not necessarily at the same time.

I see no docking and no AG on the way to Mars. So no problem with solar arrays. On the way out beyond Mars the power source would be nuclear.

Online sghill

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Re: ITS Ships Flying As a Group
« Reply #6 on: 06/20/2017 06:18 PM »
Hardly an original idea, but I see immense value in using a long nose to nose tether to create AG for the occupants. It makes designing the ITS simpler and easier for "plain old human" colonist occupancy during both cruise and surface operations.

After all, who wants 100 people to sh*t in a bag, eat out of a bag, and be too weak to function after 6 months in free-fall? Even a slow rotation will allow for functioning galleys, flushing toilets, sinks, sex, and plain old walking around for the trip's duration.

Tethers are a very old concept for space operations.  There are even conferences on the subject! http://tethersinspace2016.com/
« Last Edit: 06/20/2017 06:26 PM by sghill »
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Offline JasonAW3

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Re: ITS Ships Flying As a Group
« Reply #7 on: 06/20/2017 06:22 PM »
While hard docking the craft together is very unlikely, tethering them together seems a workable solution.

     This would facilitate actual crew transfers, should such be needed, via a space walk.  And, should something happen where one craft becomes unusable mid-flight, distributing the crew and passengers to other craft is possible, although whether or not they would still have enough Delta V to accomplish a safe landing would be problematic.

      Having one or two cargo craft ITS, that could swap out habitation modules between different craft, could be a solution, as most cargoes have a much higher tolerance for rough handling than people do.  (Yes, I'm talking swapping habitat modules and cargo pods between spacecraft in mid-flight).

      Using tethers between the craft, could, in theory, allow transfers of this sort to be done with relative safety.  (Of course, this would be relative to dying, so, there you go).

      If an ITS would have to be abandoned, then fuel transfers from the abandoned craft could be accomplished in much the same way as they would be in orbit around Earth.

      Essentially; sending groups of ITS craft, both manned and cargo as a group, would increase the safety factor significantly
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Offline Joris

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Re: ITS Ships Flying As a Group
« Reply #8 on: 06/20/2017 06:38 PM »
Bad idea to spin them or try to create artificial gravity. Creates a bunch of problems and barely gives any benefits. Remember that Elon wants to send ITS on fast trajectories, so even less reason than usual to do it on a Mars mission.
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Online guckyfan

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Re: ITS Ships Flying As a Group
« Reply #9 on: 06/20/2017 06:53 PM »
Bad idea to spin them or try to create artificial gravity. Creates a bunch of problems and barely gives any benefits. Remember that Elon wants to send ITS on fast trajectories, so even less reason than usual to do it on a Mars mission.

Agree for Mars. I was talking about going beyond.

Offline The Amazing Catstronaut

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Re: ITS Ships Flying As a Group
« Reply #10 on: 06/20/2017 07:55 PM »
We're going a wee bit off topic here with Tethered AG or any other kind of interconnected AG. If they're attached together, are they truly "flying as a group" or are they one structure for all intents and purposes?

I like the suggested idea of flying on slightly different planes so there's always somebody who can rescue you if you have a contingency in transfer. Means you don't have to waste too much propellant to rescue a stricken ITS crew and could relocate them whilst continuing the mission. Lots of opportunities to save lives there, for it lets the "fleet" be its own insurance policy.
« Last Edit: 06/20/2017 07:57 PM by The Amazing Catstronaut »
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Offline Joris

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Re: ITS Ships Flying As a Group
« Reply #11 on: 06/20/2017 08:08 PM »
If they end up flying docked together to Mars, or even near each other. They are going to be arriving at the same time. This means that either they will be flying in close proximity during the EDL, which is dangerous. Or they will be landing far apart, which I assume is not the intended goal. (I imagine they'll all want to land at the same base.)

Flying together could involve a 90 minute separation between TMI of ships though. To allow for some sort of contingency, but there's no reason to do it for luxurious reasons such as dedicated dining rooms.
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Online sanman

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Re: ITS Ships Flying As a Group
« Reply #12 on: 06/20/2017 09:54 PM »
If they end up flying docked together to Mars, or even near each other. They are going to be arriving at the same time. This means that either they will be flying in close proximity during the EDL, which is dangerous. Or they will be landing far apart, which I assume is not the intended goal. (I imagine they'll all want to land at the same base.)

Flying together could involve a 90 minute separation between TMI of ships though. To allow for some sort of contingency, but there's no reason to do it for luxurious reasons such as dedicated dining rooms.

But if the ships separate on final approach to Mars, and each ship is going to have to apply some thrust to put itself on the correct final trajectory, perhaps that's where the thrust-firing for each ship could be differentiated, to allow them to EDL at staggered intervals - say 10 minutes apart?

How far apart do ships have to be to avoid hazards from an adjacent ship exploding catastrophically?
Shouldn't 10 minutes apart be good enough when it comes to EDL? How long can explosion debris stay in the air if Mars has a near-hard vacuum? I don't see anyone worrying about returning FalconHeavy boosters harming each other, and they're probably as near as can be.
« Last Edit: 06/20/2017 09:54 PM by sanman »

Offline Kaputnik

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Re: ITS Ships Flying As a Group
« Reply #13 on: 06/20/2017 10:06 PM »
Actually docking the ships via pressuried transfer tunnels is likely unnecessary and complex. Off the top of my head you have thermal issues, line of sight for GNC equipment, load paths for thruster firings, plume impingement, and of course potential clash/overlap of deployed arrays. However it might be possible for two ITS ships to perform a docking to e.g evacuate a damaged ship, in an emergency.

Connecting two ships by tether doesn't seem necessary either,band may present some of the same problems.

With fast transfers being the plan, it will be easier to just fire off ships throughout the launch window and hunker down for the duration. Perhaps rescue missions would be possible if the ships aren't spaced too far apart. But think along the lines of old transatlantic liners rather than one big convoy.
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Offline The Amazing Catstronaut

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Re: ITS Ships Flying As a Group
« Reply #14 on: 06/22/2017 12:36 AM »
That works. I think any situation where they arrive at mars within minutes of each other whilst being closed in transit would create all kind of other problems wherin solving them would be more costly than simply not having them in the first place - although it would make for the Solar System's most iconic lightshow if you were on the surface looking up.

You can still have a "convoy" so to speak, but staggered. The smallest of distances are going to be amplified to varying degrees anyway due to the nature of the curve. You don't want them to be too close due to obvious hazards. In addition, I do wonder to what degree the influence of each ITS would slightly influence each other's trajectory. It wouldn't be much and it wouldn't be unmanageable, but adding more factors into what will be one of the most visibly complex engineering challenges of the modern world isn't a great idea. Little distinctions become significant during transfers.

That Musk repeats the term "fleet" in different media as if it's a pivotal precept rather than a way to communicate the idea of multiple ships in one window to the general public, infers an inherent value to having lots of ships arriving and departing Mars relatively simultaneously instead of spread out at times of convenience throughout the window. Simple propellant and time efficiency isn't a sufficient explanation considering ITS's margins to go out of your way to fly together, and I feel there needs to be something beyond  the chance of rescue and redundancy (whilst that in itself is extremely compelling -  if we tread out into the solar system, occasionally people are going to die in space whilst doing so. At some point, a lot of people, due to the sad inevitabilities that will build interplanetary colonisation [which Musk admits to], will die. Minimising risk is always essential).

I wonder if there may eventually be an ITS, maybe thirty or more years down the line from the start of regular-ish flights every window, if you have a whole flotilla of the craft,  there might be an ITS wherin its entire design purpose is to provide potential crisis minimisation for other ITS. When you start to talk about hundreds of spacecraft flying out together beyond Earth's sphere of influence, you start to get thinking about how you can repair your spacecraft in space if anything fails under the massive environmental variance and multi-year service lives ITS requires to operate, and to what extent that is even possible. Of course, that doesn't answer the question of need for a fleet, which I'm sure SpaceX has a response to.

From a visual perspective,  fleets are an inherently sexy idea; a flotilla of gleaming white shuttlecocks, sails (solar panels+Possible radiators) extended like the wings of blue-headed hummingbirds, coasting off together into the infinities. If somebody ever photographed it, it would become as iconic as the moonrise. Potentially much more so. Psychologically, It would probably hugely decrease the sense of being isolated with eighty plus other humans in carbon fibre can to peer out of the bow of an ITS and see just the faint gleam of another ITS somewhere in the distance, and know that your future colonymates are also out there, probably looking out for you.  If the colonial idea is going to work, future astronauts are going to have to be drawn from wider psychological stock than current astronauts. These little things matter when you're potentially giving up your house for the equivalent of a sea voyage to an unexploited continent.

Although this, of course, would be a long way into the future. If it even pans out that way.
« Last Edit: 06/22/2017 12:37 AM by The Amazing Catstronaut »
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Offline MickQ

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Re: ITS Ships Flying As a Group
« Reply #15 on: 06/24/2017 12:38 AM »
ISS orbits in about 90 minutes, right ?  So if you had 6 ITS in an equivalent type of orbit they would be
15 minutes apart.  Enough separation for TMI and cruise ?

Offline Aussie_Space_Nut

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Re: ITS Ships Flying As a Group
« Reply #16 on: 06/25/2017 01:25 AM »
Regarding a squadron of ITS arriving at the same time. Is there a showstopper reason why they can't aerobrake but then pop back up into a stable Mars orbit such that they can then choose a good time to land?

Offline whitelancer64

Re: ITS Ships Flying As a Group
« Reply #17 on: 06/25/2017 01:30 AM »
Regarding a squadron of ITS arriving at the same time. Is there a showstopper reason why they can't aerobrake but then pop back up into a stable Mars orbit such that they can then choose a good time to land?

Fuel to get back into orbit.
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Offline Aussie_Space_Nut

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Re: ITS Ships Flying As a Group
« Reply #18 on: 06/25/2017 01:39 AM »
I mean use aerobraking to slow down enough that you stay in orbit but not enough that you have to land. Dip into atmosphere, slow down enough to no longer be able to leave Mars orbit, but not so much that you have to land. In other words using very little fuel if any at all.

Offline Donosauro

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Re: ITS Ships Flying As a Group
« Reply #19 on: 06/25/2017 01:49 AM »
I mean use aerobraking to slow down enough that you stay in orbit but not enough that you have to land. Dip into atmosphere, slow down enough to no longer be able to leave Mars orbit, but not so much that you have to land. In other words using very little fuel if any at all.

You'd need, at a minimum, to do enough of a burn at apogee to raise the perigee above the atmosphere.

Offline Aussie_Space_Nut

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Re: ITS Ships Flying As a Group
« Reply #20 on: 06/25/2017 02:00 AM »
Ok. So you would need some expenditure of fuel to stabilise the orbit.

However if the squadron arrived at roughly the same time but each chose to aerobrake such that they all exited Mars atmosphere at slightly different speeds you would end up with different elliptical orbits for each ship thereby allowing different landing times for each ship. Little to no fuel required.

Online guckyfan

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Re: ITS Ships Flying As a Group
« Reply #21 on: 06/25/2017 05:05 AM »
You'd need, at a minimum, to do enough of a burn at apogee to raise the perigee above the atmosphere.

No need to get into a stable orbit. You can land on the next pass. Expend a little propellant for precision targeting of the landing area.

But I doubt this will happen with passenger ships. They may need to do two passes for the heaviest cargo with 450t because they can not bleed enough speed in one pass, being that heavy.

Offline Aussie_Space_Nut

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Re: ITS Ships Flying As a Group
« Reply #22 on: 06/25/2017 05:38 AM »
So, bottom line is a squadron of ITS ships arriving together can land at different times by choosing to aerobrake into slightly different elliptical orbits.  :)

Offline Kaputnik

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Re: ITS Ships Flying As a Group
« Reply #23 on: 06/25/2017 11:12 AM »
So, bottom line is a squadron of ITS ships arriving together can land at different times by choosing to aerobrake into slightly different elliptical orbits.  :)

I know SpaceX are good at doing the things that nobody has done before, but I still feel the need to point out that aerocapture is indeed one of the things that nobody has done before.
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Offline philw1776

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Re: ITS Ships Flying As a Group
« Reply #24 on: 06/25/2017 01:40 PM »
Even if all ITS departed "together" slight deltaV differences and/or departure times could adjust landing times by hours or even days.  No need for complex failure inviting aeromanovering operations at Mars to get differing landing times. 
The ability to get from ship to ship in an emergency would be longer in this scenario.
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Offline Hotblack Desiato

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Re: ITS Ships Flying As a Group
« Reply #25 on: 06/27/2017 04:42 PM »
I could imagine, that the ITS-crafts can be in LEO 10km apart on the same orbit. That would be a bit over a second time between each other.

When they fire up the engines for the TMI-burn they will then stay 10km apart after the burn.

This would then raise the question, whether they can dock to each other on the interplanetary flight or not. I don't see a reason why they should, but just the possibility to do so adds another layer of security, since one ITS in distress can be supported by the others, either by providing spare parts or by rescuing the crew and abandoning the craft. If they fly further apart, a mid-flight docking might not be possible.

Another advantage is, that people will tend to communicate with each other, and such a close distance means, that the signal delay is virtually irrelevant.

During reentry, they should have at least 10km distance between two crafts. This will cause other problems, such as we don't know the cross range capability of ITS inside the martian atmosphere. I wouldn't assume more than 50km cross range, which clearly limits their number of ITS landing on the same spot on the same day.

I don't fear that one ITS might blow up during reentry. The problem we should consider is the collision of two ITS during reentry and landing.

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Re: ITS Ships Flying As a Group
« Reply #26 on: 06/27/2017 06:19 PM »
I could imagine, that the ITS-crafts can be in LEO 10km apart on the same orbit. That would be a bit over a second time between each other.

When they fire up the engines for the TMI-burn they will then stay 10km apart after the burn.

They'll keep the same spacing in time, not in space.   Immediately after the TMI burn they'll be moving faster than they were in LEO so they'll have to be more than 10km apart to keep the same time separation.

Offline Hotblack Desiato

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Re: ITS Ships Flying As a Group
« Reply #27 on: 06/27/2017 08:33 PM »
I could imagine, that the ITS-crafts can be in LEO 10km apart on the same orbit. That would be a bit over a second time between each other.

When they fire up the engines for the TMI-burn they will then stay 10km apart after the burn.

They'll keep the same spacing in time, not in space.   Immediately after the TMI burn they'll be moving faster than they were in LEO so they'll have to be more than 10km apart to keep the same time separation.


True, after accelerating, the ITS-crafts should spread to 15-20km (maybe more, maybe not exactly the same trajectories, which makes correction burns necessary). But those are easily manageable distances, if one ITS needs repair or an evacuation. Accelerate 1 m/s towards another ITS, and 4h later, you're there. They even could fly within a few hundred meters to each other, the only thing they should take care of: don't bump into each other.

Online CraigLieb

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Re: ITS Ships Flying As a Group
« Reply #28 on: 06/28/2017 02:25 PM »
It would make sense that here would be small shuttles for essential exchange both in orbit prior to departure and once on the way to Mars. One might speculate that emergency repairs outside the ship while underway may demand these kinds of EVA beyond just a suit especially if large (mass/inertia/bulky) repair parts have to be taken along.   Dragon docking maneuvers experience is critical here.
The rocket scientists can figure out the delta-V requirements to move between ships in orbit. Suggest they not let the ship board computer control the pod bay doors.
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