Author Topic: MCT Speculation and Discussion Thread 4  (Read 621457 times)

Offline GORDAP

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Re: MCT Speculation and Discussion Thread 4
« Reply #2780 on: 09/18/2016 08:43 PM »
Re using MCT (or ICT...) for Ceres, Europa, etc.:  Shouldn't we be basing delta Vs on leaving from Mars orbit rather than from LEO?  And refueled in LMO from Mars sourced ISRU propellants?  How much does this extend the ICT's reach?

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2781 on: 09/18/2016 09:17 PM »
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2782 on: 09/18/2016 11:29 PM »
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.

However, refuelling in Mars orbit changes these assumptions. Launch into LEO (or HEO), refuel in LEO (or HEO), launch to Mars, aerobrake into Mars orbit (not surface), refuel from Mars ISRU prop launched into LMO (or HMO) by tugs...

Creating fuelling stations at each stepping stone breaks the rocket equation and changes our normal assumptions of spaceflight "efficiency".

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2783 on: 09/19/2016 12:17 AM »
Why go through the monkey motion in LMO  vs just landing and refuelling from a Tesla tanker truck? Fewer pieces, fewer steps.
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Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #2784 on: 09/19/2016 12:54 AM »
Fewer pieces, fewer steps.

...Less delta-v available after re-launch.
« Last Edit: 09/19/2016 05:03 AM by Paul451 »

Offline docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #2785 on: 09/19/2016 01:07 AM »
If the vehicle is split, Fagin-esque, it's also much light because the lower cargo section stays on Mars.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2786 on: 09/19/2016 07:45 AM »
It worsens it, LEO is around 4 km/s faster the LMO and your deeper in the suns gravity well too, all of that makes for a higher Oberth effect and higher velocity at infinity.

However, refuelling in Mars orbit changes these assumptions. Launch into LEO (or HEO), refuel in LEO (or HEO), launch to Mars, aerobrake into Mars orbit (not surface), refuel from Mars ISRU prop launched into LMO (or HMO) by tugs...

Creating fuelling stations at each stepping stone breaks the rocket equation and changes our normal assumptions of spaceflight "efficiency".

That sounds very inefficient, your scrubbing speed at mars that you then have to regain via propellant picked up at mars.  Having any kind of braking necessary to reach your next propellant fill up, even if it is frictional braking is going to be really bad.  But lets stop spit balling and crunch some numbers, lets say the destination is the Jovian system.  Based on this table http://www.projectrho.com/public_html/rocket/appmissiontable.php I can deduce the mars to Jupiter deltaV.

Direct from LEO we need 6.3 km/s

If we go to mars first  we can depart with just 3.6 km/s to mars and if we capture fictionally all the way to LMO, then from LMO a burn of 4.3 km/s is needed to send you on to Jupiter.  High mars orbit is 1.44 km/s above LMO so the Jupiter burn their would be 2.9 km/s from there.

That's still a total of 7.9 km/s but it is admittedly broken up into two legs which are considerably less then the single burn from LEO.  To convert that into propellant fraction at 380 ISP, at Earth you need 4.4:1 propellant to dry ratio to go to Jupiter, but to go to mars you need 1.6:1 and then at mars you need 2.1:1 to complete the journey.

So total propellant is very similar with the direct from Earth method need 19 percent more total.  The question is really one of the trades between availability of propellant at Earth and Mars, as I think propellant in mars orbit is going to be significantly more expensive then propellant in earth orbit so I think the direct approach wins.

If you think 6.3 km/s is too much for one vehicle to handle then simply depart from a high Earth orbit which will split the deltaV very nicely into 3.2 and 3.1 which gets you virtually the same departure burn that you would have needed from high mars orbit, which proves my point their is no advantage to falling into the mars gravity well if your destination is an outer planet.

But the whole idea is really moot anyway cause it would take lots more delta v then is viable upon arrival to just land on a moon like Callisto, Titan would be do able with aero-braking and direct decent but we are not going to send people out that far in any kind of conceivable time frame.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2787 on: 09/19/2016 11:24 AM »

That sounds very inefficient, your scrubbing speed at mars that you then have to regain via propellant picked up at mars.  Having any kind of braking necessary to reach your next propellant fill up, even if it is frictional braking is going to be really bad.  But lets stop spit balling and crunch some numbers, lets say the destination is the Jovian system.  Based on this table http://www.projectrho.com/public_html/rocket/appmissiontable.php I can deduce the mars to Jupiter deltaV.

Direct from LEO we need 6.3 km/s

If we go to mars first  we can depart with just 3.6 km/s to mars and if we capture fictionally all the way to LMO, then from LMO a burn of 4.3 km/s is needed to send you on to Jupiter.  High mars orbit is 1.44 km/s above LMO so the Jupiter burn their would be 2.9 km/s from there.

That's still a total of 7.9 km/s but it is admittedly broken up into two legs which are considerably less then the single burn from LEO.  To convert that into propellant fraction at 380 ISP, at Earth you need 4.4:1 propellant to dry ratio to go to Jupiter, but to go to mars you need 1.6:1 and then at mars you need 2.1:1 to complete the journey.

So total propellant is very similar with the direct from Earth method need 19 percent more total.  The question is really one of the trades between availability of propellant at Earth and Mars, as I think propellant in mars orbit is going to be significantly more expensive then propellant in earth orbit so I think the direct approach wins.

If you think 6.3 km/s is too much for one vehicle to handle then simply depart from a high Earth orbit which will split the deltaV very nicely into 3.2 and 3.1 which gets you virtually the same departure burn that you would have needed from high mars orbit, which proves my point their is no advantage to falling into the mars gravity well if your destination is an outer planet.

But the whole idea is really moot anyway cause it would take lots more delta v then is viable upon arrival to just land on a moon like Callisto, Titan would be do able with aero-braking and direct decent but we are not going to send people out that far in any kind of conceivable time frame.

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.  Various combinations thereof, possibly dropping off small landing vehicle payloads of several tons. Expensive but clearly matching the name of ITS.  Would need a nuclear power source that far out but ITS should have the cargo hold space to fit one.  Cut the nominal 100T cargo payload to some lower # to pick up delta V.
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Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #2788 on: 09/19/2016 02:38 PM »
Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

Venus it is then. It's the easiest place to colonize anyway.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2789 on: 09/19/2016 03:10 PM »
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.
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Offline Oli

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Re: MCT Speculation and Discussion Thread 4
« Reply #2790 on: 09/19/2016 04:17 PM »
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.

Ceres? With chemical propulsion?

The moon is certainly possible, though lunar ISRU (water ice) would clearly favor hydrolox (from what I remember).

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.

Sending cargo one-way doesn't require a vehicle like MCT. There's no need to land the entire Earth departure stage and the heat shield if they're not needed to get back. That said, an aeroshell of similar size is still required. For Venus colonization for example, I would expect payloads to go one way with expendable aeroshells.
 
« Last Edit: 09/19/2016 04:29 PM by Oli »

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2791 on: 09/19/2016 05:49 PM »
Who said purely chemical propulsion? It could be done (I could show you if you like), but I'm not going to say SpaceX has ruled it out yet!
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2792 on: 09/19/2016 06:36 PM »
Land on Ceres or the Moon. Musk had earlier made reference to landing MCT on the Moon. Ceres would be similar.

The landing thrust is not necessarily a big problem. You can do a burn above the surface and cut off thrust at just the right moment and fall the rest of the way, perhaps using RCS thrusters to finetune the landing.

Ceres? With chemical propulsion?

The moon is certainly possible, though lunar ISRU (water ice) would clearly favor hydrolox (from what I remember).

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.

Sending cargo one-way doesn't require a vehicle like MCT. There's no need to land the entire Earth departure stage and the heat shield if they're not needed to get back. That said, an aeroshell of similar size is still required. For Venus colonization for example, I would expect payloads to go one way with expendable aeroshells.

Of course it doesn't.
Just showing that the spacecraft formerly known as MCT or BFS has the capability.  It meets the "ITS" claim.
Certainly not optimal or purpose built for such missions as far as we know.

Think about this. 
What other craft claimed to be under development could actually get 10s of tonnes to the aforementioned destinations in its claimed configuration?
« Last Edit: 09/19/2016 06:38 PM by philw1776 »
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Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #2793 on: 09/19/2016 06:41 PM »
The problem with Ceres is the extra delta V for out of plane xfer.  However, slowing down @Ceres does not need delta V again for plane change.  I have not run the #s myself to see what a cargo tonnes reduction offers in increased delta V in a Ceres scenario.
« Last Edit: 09/19/2016 06:43 PM by philw1776 »
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2794 on: 09/19/2016 09:45 PM »

The spacecraft formerly known as MCT could be purchased by some future billionaire or government space agency to land a large cargo payload on Titan's surface or just aerobrake at Titan and land on say, Enceladus.  Various combinations thereof, possibly dropping off small landing vehicle payloads of several tons. Expensive but clearly matching the name of ITS.  Would need a nuclear power source that far out but ITS should have the cargo hold space to fit one.  Cut the nominal 100T cargo payload to some lower # to pick up delta V.

While a one way unmanned expendable landing on Titan seems technologically plausible, I don't think it fulfills the 'C' keyword colonial anymore.  Of course the transit time to Saturn blows any hope of amortization away so their is little point in getting the vehicle back if it is unmanned.


Is he talking about the asteroid belt or something, I can't see the landing vehicle with it's normal atmospheric EDL profile being appropriate on any other planetary body in the solar system other then Venus. 

Venus it is then. It's the easiest place to colonize anyway.

I am one that believes is unfairly overlooked to do to 'surfacism' and I find concepts like Landis2land and HAVOC plausible, deploying large balloons to float in the Venusian atmosphere at an altitude with a hospitable temperature and sunlight.  But it is likely better to just drop a full functional habitats directly into the atmosphere rather then employ a vehicle to carry it.

The problem with Ceres is the extra delta V for out of plane xfer.  However, slowing down @Ceres does not need delta V again for plane change.  I have not run the #s myself to see what a cargo tonnes reduction offers in increased delta V in a Ceres scenario.

The plane change is just icing on the cake, the real problem is that the tiny gravity wells give you almost no Oberth benefit when capturing.  The DeltaV to land on Vesta from LEO is 8.7 km/s, from LMO it's considerably better at 4 km/s.  The other large asteroids are slightly harder to reach as Vesta is one of the easier ones. 

So going from mars out to an asteroid is just barely plausible if you have the ability to fill up in mars orbit, and can tolerate a 500 day transit.  Return would likely be directly to Earth.

Offline CuddlyRocket

Re: MCT Speculation and Discussion Thread 4
« Reply #2795 on: 09/19/2016 10:55 PM »
I am one that believes is unfairly overlooked to do to 'surfacism' and I find concepts like Landis2land and HAVOC plausible, deploying large balloons to float in the Venusian atmosphere at an altitude with a hospitable temperature and sunlight.

Plausible? Theoretically, perhaps. Practical? In the light of today's engineering knowledge and industrial infrastructure, very questionable! The same goes for Lunar water-ice mining; Martian orbital propellant depots; O'Neill habitats etc. One day, we might see some or all of these things - though by 'we', I mean humanity; I don't expect to see many, if any, of these in my lifetime.

What's the strategy for bringing any of these things into existence; other than a Kennedy-esque program involving the spending of large amounts of public money - a plan fraught with potential political pitfalls! (One of Musk's strengths is his ability to see the practical, profitable steps between the here and now and his future goals.)

In any event, none of these things seem to be within the ambit of SpaceX's activities or plans, so should be discussed in other, more appropriate parts of the forum!

Offline ciscosdad

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Re: MCT Speculation and Discussion Thread 4
« Reply #2796 on: 09/20/2016 12:10 AM »
In my view, the MCT system (or whatever its to be called) will initially perform refuelling in low earth orbit. '
Later if demand requires it or the performance is needed, then a depot at L1, L2 or somewhere else at the edge of our gravity well.
The decision will be based on infrastructure cost. Fuel depots are relatively simple, but will be costly, as is all space based devices.
Given the amazing usefulness of this system, I expect rapid expansion of the fleet and its capabilities. Missions to Ceres, Vesta or anywhere beyond Mars will increasingly demand the higher performance

my 2c


Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #2797 on: 09/20/2016 12:15 AM »
I love how Venus is viewed as somehow easier to colonize by people fond of contrarian theories. It might be POSSIBLE to colonize, but no way in heck is it easier. Please try, though. May a thousand flowers bloom!
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #2798 on: 09/20/2016 01:16 AM »
I wouldn't say it is easy, I'd say that mars colonization difficulty is just massively under-estimated. 

Their is a belief that planetary surfaces are easy source of resources but I contend that mining and processing solid surfaces is the least desirable means of acquiring resources.  Atmospheric processing is preferable both for propellant production and producing chemical feed stocks for life-support and manufacturing.  So my low assessment of the value of surfaces puts Mars and Venus on roughly equal footing as the Venusian gravity well dose present significant difficulty in return to Earth which balance it's higher solar flux, radiation protection, temperature, pressure and more frequent launch opportunities and lower transit times.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #2799 on: 09/20/2016 05:18 AM »
MCT, including all the technologies necessary to get to Mars and back, is a starting point for serious planetary exploration.  There are only very limited things you get to think about with planetary exploration if you're confined to existing launch vehicles and no propellant depots.   A fully reusable MCT that gets fully refueled in LEO permits you to bring a payload somewhere in the 300-1000 ton class to Earth escape velocity.  If that payload is itself a multi-stage rocket, it opens up the possibility to send sizable probes to a great number of places on (high-thrust chemical) mission timeframes that fit within a principal investigator's career length, and low-thrust missions that send massive quantities of hardware on longer journeys.

Refuel fully in high Earth orbit with an expendable MCT, and you can start thinking about things like Main Belt, Jupiter Moon, and Saturn Moon sample returns.
« Last Edit: 09/20/2016 05:28 AM by Burninate »

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