Author Topic: Lunar Gateway Debate  (Read 138622 times)

Offline spacenut

  • Senior Member
  • *****
  • Posts: 5181
  • East Alabama
  • Liked: 2587
  • Likes Given: 2895
Re: Lunar Gateway Debate
« Reply #20 on: 07/22/2018 03:12 am »
Existing rockets can reach LL1 with decent payloads, human capsules, and various potential lunar landers. 

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 500
  • Likes Given: 1096
Re: Lunar Gateway Debate
« Reply #21 on: 07/22/2018 08:19 am »
I've been a die hard fan of the Gateway concept in its varied shapes since its inception in 1999. What bothers me with LOP-G
- no clear role
- SLS-Orion are too expensive, and LOP-G is only "cannon fodder" to provide SLS with payloads
- Distant Retrograde Orbit: EML-1 and EML-2 are better, as underlined in another post.

It is a shame, because (I will seek an earlier post of mine) there really are boatload of missions that could be done from an EML-2 Gateway, a multirole platform. From telescope servicing to GEO cleanup, and many other.
Oh well, see my post on the other thread (before it was moved to the space policy section)

https://forum.nasaspaceflight.com/index.php?topic=45240.msg1810063#msg1810063

Then again, the ISS started completely and entirely wrong (Freedom - Alpha - Fred) yet, since 2010, it had proved its worth - see Ed Kyle post, he is perfectly right. NASA really turned lemons (Freedom) into lemonade (current ISS).
« Last Edit: 07/22/2018 08:23 am by Archibald »
Han shot first and Gwynne Shotwell !

Offline TrevorMonty

Re: Lunar Gateway Debate
« Reply #22 on: 07/22/2018 10:20 am »
I've been a die hard fan of the Gateway concept in its varied shapes since its inception in 1999. What bothers me with LOP-G
- no clear role
- SLS-Orion are too expensive, and LOP-G is only "cannon fodder" to provide SLS with payloads
- Distant Retrograde Orbit: EML-1 and EML-2 are better, as underlined in another post.

It is a shame, because (I will seek an earlier post of mine) there really are boatload of missions that could be done from an EML-2 Gateway, a multirole platform. From telescope servicing to GEO cleanup, and many other.
Oh well, see my post on the other thread (before it was moved to the space policy section)

https://forum.nasaspaceflight.com/index.php?topic=45240.msg1810063#msg1810063

Then again, the ISS started completely and entirely wrong (Freedom - Alpha - Fred) yet, since 2010, it had proved its worth - see Ed Kyle post, he is perfectly right. NASA really turned lemons (Freedom) into lemonade (current ISS).
The Gateway is not locked into an orbit for life, it can move around cislunar space. Thats main reason for such capable propulsion module.

Offline TripleSeven

  • Full Member
  • ****
  • Posts: 1145
  • Istanbul Turkey and Santa Fe TEXAS USA
  • Liked: 588
  • Likes Given: 2095
Re: Lunar Gateway Debate
« Reply #23 on: 07/22/2018 10:50 am »
Here is my take. LEO is a better place for commercialization. Smaller rockets are easier to fund and develop and reusability is easier from LEO than from deep space.

As presented there really isn’t enough for commercial to do. Too few flights needed. I am not against a station near the moon, but I fear that instead of an additional destination to go to it becomes the ISS replacement and human spaceflight gets reduced to nothing more than one flight every other year or 2 flights per year that only stay in space for a few weeks. Compared to the ISS that is a great reduction of capability. The ISS gets about 4 cargo flights a year and this thing looks like it might only need 1-2. In addition the ISS is planned to get another 2 flights per year from each provider for crew. If SLS launches the crew then there is no work for commercial to do in terms of crew.

As for international partners they have their own objectives in space and ESA, Japan, Canada would be willing to go almost anywhere NASA would. I don’t see any advantage here at all. In fact I dare say that this would be something that slows it down as each partner adds their own requirements.

I also don’t like the reusable lander. I love reusability, but I see no such item.  The problem with a lander is that most of the mass is propellant and I see no plan to cheaply send propellant to this station. I see no use of say a SEP tug and a smaller rocker to send a tanker to the station or the use of BFR(or something like it) to send and retrieve a lander from the station for servicing on Earth. The tanker craft will need to cost substantial less than the lander in order for it to make any sense and the launch costs are going to be about the same for sending the tanker as sending the lander, so how does reusability save money in this instance? The tanker is going to need many of the same systems as the lander so making it much cheaper is going to be hard.

My theory on landers is that they need to smaller rather than larger...and attach to some ground base infrastructure

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: Lunar Gateway Debate
« Reply #24 on: 07/22/2018 01:15 pm »
Time has a balanced article discussing the pluses and minuses of the Lunar Gateway....
http://time.com/5342743/nasa-moon-mars/

A couple of concrete errors in the Time article:

* Orion is described as "similar to the old Apollo, but significantly bigger and more capable."  Delta-V being a key measure of a spacecraft's capability, it's a stretch to that Orion is flat out more capable than Apollo, even if it can support a larger crew for a longer period.

* "For the first time in five decades, the U.S.–along with private-industry and international partners–has committed itself to returning to the moon, and to doing it on a defined timeline."  Aside from wishful thinking expressed by NASA and contractors, no timeline has been established.  In fact, Pres. Trump's Space Policy Directive 1 (referenced in the article and attached below) specifically removes even the loose timeline established in Obama's Presidential Policy Directive 4 (also attached).

But the biggest problem is that whole idea of NASA could be landing people on the moon 8 years from now is absurd from a budget perspective.  The existing Orion/SLS budget line will be fully utilized just to fly a crew to a gateway once per year, and ISS shows every sign of living until 2028.  The Europeans are already tapped out in that they're paying for Orion's ESM.

If humans go from LOP-G to the lunar surface on a time-scale anything like that discussed in the article, my money would be on it being done by Blue Origin, not NASA.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: Lunar Gateway Debate
« Reply #25 on: 07/22/2018 01:28 pm »
A 'Lunar Gateway' would only be a 'success' or useful if it included a small/medium propellant depot for a reusable, crewed Lander that was based there. And because of the Lander; it would have to have the right orbit to allow good access and coverage to much of the Lunar surface for useful periods of time - could someone nail down for me/us what type of orbit that would be?

Without a Lander based there, I'd say the Gateway serves little purpose...
A refueling station is needed for a reusable lander.  Agreed.  The station would also have to support the lander in other ways.  Cargo transfer.  Human transfer and temporary habitation.  Maintenance and testing.

I'm not so sure about that.  Assuming lander propellant comes from earth and not from the moon, maybe the lander simply docks with a tanker, propellant is transferred and then tanker and lander go their separate ways, no station needed.  Ditto for human transfer.

If the point is to build a base on the surface, wouldn't you likely do maintenance there?  If no surface base is foreseen and the plan is sorties globally, then maybe the case for high-orbit station increases.  But, given that just operating LOP-G, never mind funding landers or surface operations, will likely cost over $3 billion a year, you have to ask whether it is a net benefit.

« Last Edit: 07/22/2018 01:34 pm by Proponent »

Offline Oli

  • Senior Member
  • *****
  • Posts: 2467
  • Liked: 605
  • Likes Given: 60
Re: Lunar Gateway Debate
« Reply #26 on: 07/22/2018 01:33 pm »
LOP-G looks like a big compromise to me:

- It gives SLS/Orion something to do.
- It's far cheaper than an outpost on the lunar surface.
- The modular structure allows for contributions by international/commercial partners.
- From a science POV it actually seems relatively useful. Again, given the budget limitations.

I think orbital outposts are the future of government-funded human spaceflight BEO. Going down to the surface is just too much of a PITA.
« Last Edit: 07/22/2018 01:34 pm by Oli »

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 5362
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 2239
  • Likes Given: 3883
Re: Lunar Gateway Debate
« Reply #27 on: 07/22/2018 01:36 pm »
Orion is great but for two things: it's a little too heavy and it's propellant load is a little too small; which of course, limits delta-v capability. The craft should have been able to insert itself and a payload into and then leave lunar orbit by itself, as Apollo could. By all means have a bit more internal volume than Apollo: Apollo CM had about 70 cubic feet per crew member. Assuming that Orion was definitely a 4x crew vehicle and using the same ratio per person, this would give 280 cubic feet habitable volume. I wonder what sort of diameter the Orion CM would then have to be - not 5 meters as it is now - to achieve that 280 cubic feet value approximate value? 4.2 meters? 4.3? The habitable volume of Starliner, which is 4.56 meters is 390 cubic feet (11 cubic meters) and Dragon is 350 cubic feet (10 cu meters). Both of those Command capsules are much lighter than the Orion; which is 10 metric tons just for the Command Module!! I wonder how much lighter it would have been if it had been limited to a diameter under 4.5 meters? A lot less, or just a little?
« Last Edit: 07/22/2018 01:37 pm by MATTBLAK »
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline MATTBLAK

  • Elite Veteran & 'J.A.F.A'
  • Senior Member
  • *****
  • Posts: 5362
  • 'Space Cadets' Let us; UNITE!! (crickets chirping)
  • New Zealand
  • Liked: 2239
  • Likes Given: 3883
Re: Lunar Gateway Debate
« Reply #28 on: 07/22/2018 01:39 pm »
A 'Lunar Gateway' would only be a 'success' or useful if it included a small/medium propellant depot for a reusable, crewed Lander that was based there. And because of the Lander; it would have to have the right orbit to allow good access and coverage to much of the Lunar surface for useful periods of time - could someone nail down for me/us what type of orbit that would be?

Without a Lander based there, I'd say the Gateway serves little purpose...
A refueling station is needed for a reusable lander.  Agreed.  The station would also have to support the lander in other ways.  Cargo transfer.  Human transfer and temporary habitation.  Maintenance and testing.

I'm not so sure about that.  Assuming lander propellant comes from earth and not from the moon, maybe the lander simply docks with a tanker, propellant is transferred and then tanker and lander go their separate ways, no station needed.  Ditto for human transfer.

If the point is to build a base on the surface, wouldn't you likely do maintenance there?  If no surface base is foreseen and the plan is sorties globally, then maybe the case for high-orbit station increases.  But, given that just operating LOP-G, never mind funding landers or surface operations, will likely cost over $3 billion a year, you have to ask whether it is a net benefit.


Orion/SLS (Block 1B) is supposed to have a 'surplus', co-manifested payload ability of about 10 metric tons. Perhaps the Orion could bring a tanker module with it each time to refuel a reusable Lander? Just an idea...
"Those who can't, Blog".   'Space Cadets' of the World - Let us UNITE!! (crickets chirping)

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: Lunar Gateway Debate
« Reply #29 on: 07/22/2018 01:43 pm »
LOP-G looks like a big compromise to me:

- It gives SLS/Orion something to do.
- It's far cheaper than an outpost on the lunar surface.
- The modular structure allows for contributions by international/commercial partners.
- From a science POV it actually seems relatively useful. Again, given the budget limitations.

What scientific benefits do you see?

We hear about tele-operated rovers on the lunar surface.  I can see why a low-latency link to a controller on LOP-G would be helpful, but, when we have self-driving cars on Earth coping for the most part successfully with moving hazards (other vehicles and pedestrians), I struggle to imagine that it's a great advantage in the moon's very static environment.

You get to soak astronauts in the interplanetary radiation field, which you can't do on ISS.  But only for about six weeks at a time, so I'm not sure it's all that relevant to preparing for missions to Mars.

EDIT:  Capitalized "Earth" and added missing "with"
« Last Edit: 07/22/2018 03:24 pm by Proponent »

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 500
  • Likes Given: 1096
Re: Lunar Gateway Debate
« Reply #30 on: 07/22/2018 02:52 pm »
how much delta-v does the ppm provides ?
Han shot first and Gwynne Shotwell !

Offline TripleSeven

  • Full Member
  • ****
  • Posts: 1145
  • Istanbul Turkey and Santa Fe TEXAS USA
  • Liked: 588
  • Likes Given: 2095
Re: Lunar Gateway Debate
« Reply #31 on: 07/22/2018 02:57 pm »
LOP-G looks like a big compromise to me:

- It gives SLS/Orion something to do.
- It's far cheaper than an outpost on the lunar surface.
- The modular structure allows for contributions by international/commercial partners.
- From a science POV it actually seems relatively useful. Again, given the budget limitations.

What scientific benefits do you see?

We hear about tele-operated rovers on the lunar surface.  I can see why a low-latency link to a controller on LOP-G would be helpful, but, when we have self-driving cars on earth coping for the most part successfully moving hazards (other vehicles and pedestrians), I struggle to imagine that it's a great advantage in the moon's very static environment.

You get to soak astronauts in the interplanetary radiation field, which you can't do on ISS.  But only for about six weeks at a time, so I'm not sure it's all that relevant to preparing for missions to Mars.

of all the "good things" the notion of low latency link to a controller seems like the most made up one

not only for the reasons you mention, (which as you point out is dealt with handily by vehicles on and flying above and below the sea on earth) but also in that it goes the opposite way from where "things" are going on earth to use robotic vehicles

what it does is put yet another "layer" between the people who should be using the drone to do things...and the drone.  In addition it puts a premium on the person at the Gateway who is controlling the drone...and since this person does not work 24 hours a day...a limitation on the drones operation.

we should be putting the operation of the "drones" closer to the people who are actually using them, not farther away

Offline Proponent

  • Senior Member
  • *****
  • Posts: 7277
  • Liked: 2782
  • Likes Given: 1462
Re: Lunar Gateway Debate
« Reply #32 on: 07/22/2018 03:10 pm »
Orion/SLS (Block 1B) is supposed to have a 'surplus', co-manifested payload ability of about 10 metric tons. Perhaps the Orion could bring a tanker module with it each time to refuel a reusable Lander? Just an idea...

Hmmm.....  The Apollo LM's total propellant load (ascent and descent stages together) was about 11 tonnes.  An Apollo-style lander today could no doubt get away with less propellant by saving weight and burning, say, lox/methane or maybe even lox/hydrogen rather than NTO/Aerozine 50.  But the dry weight of the LM's ascent stage was less than a quarter that of the descent stage.  If you want a reusable lander, you're going to have to haul something roughly equivalent to the descent stage all the way from the surface back to the staging point, and that means burning a lot more propellant.  That propellant itself needs to be landed on the moon in the first place, so we're talking about a much larger vehicle.

Then there's the fact that, delta-V-wise, LOP-G is about 700 m/s further (one way) from the lunar surface than was the Apollo LM when it began its descent from LLO.

So I don't think Orion/SLS's 10-tonne co-manifested payload capability helps much for fueling a crewed lander.
« Last Edit: 07/22/2018 03:17 pm by Proponent »

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
Re: Lunar Gateway Debate
« Reply #33 on: 07/22/2018 03:17 pm »
of all the "good things" the notion of low latency link to a controller seems like the most made up one

Lunkakhod drove quite a long way indeed, using ridiculously long latency. significantly over 2*triptime, due to the long frame transmit time, and despite only being able to drive a small fraction of the time due to comms and other constraints.

It is somewhat arguable that reducing delay by having nearby astronauts to do teleoperation has a benefit for Mars.
For the moon - well - no.

Shipping nice high-res images, with depth information from LIDAR, a good framerate, and building this into a centimeter accurate 3d model of the upcoming 20m or so is very tractable today with almost off the shelf hardware and software.
This would make the drivers task orders of magnitude easier than Lunakhod.

And of course, you can get people on earth to do this for well under $100/hr.
Comms is of course something that's needed. I note China already has a farside comsat in place.

Offline RonM

  • Senior Member
  • *****
  • Posts: 3340
  • Atlanta, Georgia USA
  • Liked: 2231
  • Likes Given: 1584
Re: Lunar Gateway Debate
« Reply #34 on: 07/22/2018 04:33 pm »
- It gives SLS/Orion something to do.

As long as Congress wants to keep funding SLS it needs something to do. LOP-G is a reasonable idea since it uses the leftover capacity of Block 1A and Orion. If Congress cancels SLS, and there's no reason to think that will happen anytime soon, then LOP-G loses its "free" ride.

- It's far cheaper than an outpost on the lunar surface.

True, but it's not nearly as useful. It could lead to a lunar outpost or reusable landers since those would be expanding on an existing project, as opposed to trying to fund direct missions. Got to get Congress to sign the check.

- The modular structure allows for contributions by international/commercial partners.

This is the best part of LOP-G, assuming it's worth building it in the first place.

- From a science POV it actually seems relatively useful. Again, given the budget limitations.

Big lunar science can be done from individual orbiters, but smaller projects can't afford it. LOP-G can be used like ISS with experiments added to the station to take advantage of the existing power and data resources. Less expensive for the researchers.

of all the "good things" the notion of low latency link to a controller seems like the most made up one

Agreed. Modern technology would allow a rover to avoid mishaps the short control delay from Earth might introduce. Controlling rovers from a crewed orbital station is a good idea for beyond cislunar space, such as at Mars, Venus, etc.

Offline ncb1397

  • Senior Member
  • *****
  • Posts: 3497
  • Liked: 2310
  • Likes Given: 29
Re: Lunar Gateway Debate
« Reply #35 on: 07/22/2018 04:53 pm »
Orion/SLS (Block 1B) is supposed to have a 'surplus', co-manifested payload ability of about 10 metric tons. Perhaps the Orion could bring a tanker module with it each time to refuel a reusable Lander? Just an idea...

Hmmm.....  The Apollo LM's total propellant load (ascent and descent stages together) was about 11 tonnes.  An Apollo-style lander today could no doubt get away with less propellant by saving weight and burning, say, lox/methane or maybe even lox/hydrogen rather than NTO/Aerozine 50.  But the dry weight of the LM's ascent stage was less than a quarter that of the descent stage.  If you want a reusable lander, you're going to have to haul something roughly equivalent to the descent stage all the way from the surface back to the staging point, and that means burning a lot more propellant.  That propellant itself needs to be landed on the moon in the first place, so we're talking about a much larger vehicle.

Then there's the fact that, delta-V-wise, LOP-G is about 700 m/s further (one way) from the lunar surface than was the Apollo LM when it began its descent from LLO.

So I don't think Orion/SLS's 10-tonne co-manifested payload capability helps much for fueling a crewed lander.

The Apollo LM did things this wouldn't necessarily have to do like carry a rover. With LOX/H2 fuel, you could potentially get away with 10 metric tons of propellant with the following specifications:

fuel: 10,000 kg
payload: 1500 kg (crew environment, equivalent to dry mass of Cygnus version 1)
stage dry mass: 2700 kg
stage fueled dry fraction : 21%
total vehicle fueled dry fraction: 30%
isp: 430 (middle of the road LOX/H2 performance)
delta -v: 5133 m/s

IIRC, 30% dry fraction is about where Shuttle was when you consider the combined orbiter and fuel tank. There likely is some version of these numbers for other fuels as well. This gives you a lander that can potentially launch crew and cargo, have compatibility with a range of launch vehicle sizes down to around Atlas V and up to SLS (with  payloads to the surface scaling accordingly) and operate in a reusable mode with the gateway for crew or light payloads. 

edit: It seems I didn't remember correctly. Shuttle tank with a gross mass of 760,000 kg, dry mass of 26,500 kg and the orbiter with a dry mass of 68,585 kg gives a dry mass fraction of 11.5%(95,085 kg / 828,585 kg).

edit 2: I forgot at least two space-suited individuals at 150 kg each which drops the delta v by 200 m/s so ISP has to go to 440(still 8 seconds less than J-2x) and you have to save 100 kg somewhere else to get back over 5100 m/s. Worse outcome is you need a 3000 kg shipment equivalent to an ISS cargo resupply to get the extra water to generate the extra fuel(electrolysis is commonly done on ISS so I see no technical hurdles here).

edit 3: After looking at hydrogen engines that exist, it seems nearly every hydrolox engine out there (even the upper stage ones) are too big for this application (assuming you want to land on main engines at close to 1 thrust to weight ratio). It is too bad that one of the smallsat launchers doesn't have a hydrolox upper stage as a cluster of something sized for that might work. So, we are looking at a new engine, albeit very small.

edit 4: Looking at hypergolics, you need the following specifications:

fuel: 10,000 kg
payload: 1400 kg (crew environment, equivalent to dry mass of Cygnus version 1) + 300 kg crew, 1700 kg
stage dry mass: 900 kg
stage fueled dry fraction : 8.3%
total vehicle fueled dry fraction: 18.7%
isp: 330
delta -v: 5103 m/s

So, the propulsion portion needs to carry same amount of fuel as the lunar descent module but weigh about half as much. But looking at the descent module layout, there probably was quite a bit of room for weight savings:



You wouldn't use something like the hypergolic common bulkhead on the proton 2nd stage for something manned, but two tanks stacked one on top of each other with a separation wall might be a happy medium.
« Last Edit: 07/23/2018 08:43 pm by ncb1397 »

Offline butters

  • Senior Member
  • *****
  • Posts: 2399
  • Liked: 1693
  • Likes Given: 598
Re: Lunar Gateway Debate
« Reply #36 on: 07/22/2018 05:48 pm »
A cislunar gateway station makes sense as one of the last pieces of the transportation architecture, after lunar surface spacecraft are already using lunar ISRU propellant for the return trip. Making it the first piece of infrastructure is like building container ports before clipper ships.

Delivering terrestrial propellant to a cislunar station is big PITA compared to LEO. A lunar lander based at LOP-G would be cryogenic, probably hydrolox. The only conceivable providers would be ULA with ACES and Blue Origin with TBD. The ACES tanker would be expendable and would have a cost disconcertingly close to that of an EUS. Who knows what Blue could bring to the table in terms of a long-coast cryogenic tanker, but reusability seems doubtful.

These tanker missions are going to be expensive, there may not be more than one capable provider, and the NewSpace players will struggle to identify how developing to these requirements could be helpful for their proprietary roadmaps.

If we're going to be pushing an expendable ACES full of propellant out to cislunar orbit, then we might as well give it the landing accessories from the DTAL concept and just land it on the darn surface.
« Last Edit: 07/22/2018 05:50 pm by butters »

Offline oldAtlas_Eguy

  • Senior Member
  • *****
  • Posts: 5305
  • Florida
  • Liked: 5005
  • Likes Given: 1444
Re: Lunar Gateway Debate
« Reply #37 on: 07/22/2018 07:10 pm »
A cislunar gateway station makes sense as one of the last pieces of the transportation architecture, after lunar surface spacecraft are already using lunar ISRU propellant for the return trip. Making it the first piece of infrastructure is like building container ports before clipper ships.

Delivering terrestrial propellant to a cislunar station is big PITA compared to LEO. A lunar lander based at LOP-G would be cryogenic, probably hydrolox. The only conceivable providers would be ULA with ACES and Blue Origin with TBD. The ACES tanker would be expendable and would have a cost disconcertingly close to that of an EUS. Who knows what Blue could bring to the table in terms of a long-coast cryogenic tanker, but reusability seems doubtful.

These tanker missions are going to be expensive, there may not be more than one capable provider, and the NewSpace players will struggle to identify how developing to these requirements could be helpful for their proprietary roadmaps.

If we're going to be pushing an expendable ACES full of propellant out to cislunar orbit, then we might as well give it the landing accessories from the DTAL concept and just land it on the darn surface.
ACES other then its RL-10 engines is potentially the cheapest expendable US. If AJR is able to decrease costs of RL10C-X as much as they are indicating (up to ~1/2 the current costs), a ACES tanker or even the ultimate of a ACES derived DTAL could be the cheapest and quickest way to the Lunar surface. Much of the solutions have been under study for the last decade. This low costs is because of several factors. The first is the stainless steel balloon tank of the ACES is still the cheapest tank to manufacture ever. As a comparison to EUS is that the rate is that of 5 to 10 or molre per year to EUS  of ~1/year. Another factor is the IVF tech of ACES reduces the total hardware and hardware costs. Leaving only the engines as the major cost driver but even here the decision to use the new design/manufacture process RL10C-X also reduces costs for ACES further.

The only actual detractor is the cost of the Vulcan to get ACES into orbit.

But what if BO and ULA collaborate on using ACES as a third stage/tanker on top of the NG then you could easily deliver as much as 20mt of cryo prop to the LOP-G location per NG flight. So it is possible in this case to deliver 20mt of cryo prop to LOP-G for under $100M each trip. And the plus is that the ACES is a miniature Depot such that operationally there are tremendous number of options available to mission planners with this capability.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
Re: Lunar Gateway Debate
« Reply #38 on: 07/22/2018 11:34 pm »
Delivering terrestrial propellant to a cislunar station is big PITA compared to LEO. A lunar lander based at LOP-G would be cryogenic, probably hydrolox. The only conceivable providers would be ULA with ACES and Blue Origin with TBD. The ACES tanker would be expendable and would have a cost disconcertingly close to that of an EUS. Who knows what Blue could bring to the table in terms of a long-coast cryogenic tanker, but reusability seems doubtful.
'Only conceivable' ?

It is not unreasonable to have schedule and other doubts about BFS, but to dismiss it against 'TBD' seems at best pessimistic.

BFS, with 8 launches, including one used as a tanker, gets you a hundred tons to the surface and substantial payload back.
(fill tanks in LEO, top off in HEO, TLI, meet up with tanker already in LLO, transfer fuel, land, rendevous, take on TEI fuel, burn for earth).

The BFS is using 55 tons to ascend to 85 tons dry over 1800m/s, and 150 tons to descend with that 100 tons of payload.
This is at ISP of 370, and 85 tons dead weight.
Call it 200 tons of propellant.
If we imagine a hydrolox stage using that 200 tons, with 20 tons dry, it would take 10 tons to ascend, payload would go up to 160 tons from 100. (not quite this good, as the extra payload and H2 tanks cut into the mass).

The cost to SpaceX of the first option is around $40M for 100 tons down.

The cost of a whole BFS in LLO semi-permenantly is according to IAC 2016/7 figures likely to be under $200M.

Cost, is of course, not price.
A very small hydrolox thruster to do TEI using the existing hydrogen tank the second architecture requires anyway would defray the H2 tank mass cost.

As one data point, Apollo lander had about 11 tons of fuel. To get that into LLO would cost one falcon heavy launch in expendable mode, with a disposable dragon for guidance, and a large tank taking place of the trunk, using near-off-the-shelf commercial earth grade tanks with insulation for some months stay. (assuming a mass fraction of a third for the tanks).
That is at least a cap on pricing of fuel  in LLO. - around $10M/ton.
There are certainly much better ways to do this, but if your landers amortised cost is not well under $100M/mission, cheaper fuel (hypothetically available from some lunar station with a clever architecture) does not help.
« Last Edit: 07/23/2018 12:12 am by speedevil »

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8906
  • South coast of England
  • Liked: 500
  • Likes Given: 223
Re: Lunar Gateway Debate
« Reply #39 on: 07/23/2018 12:04 am »
Personal opinion. I believe that one of the main tasks of a lunar space station will be to help build the Moon base(s).

Many houses are built out of 9 inch bricks. Each brick could be taken to the site individually by marathon runners but construction companies prefer to buy a truck and deliver a ton of bricks in one go. So to reduce construction time there will be strong pressure to make the lunar base out of large (heavy) modules. (See attached picture of a lorry carrying bricks.)

The nearest approximation to construction of a Moon base is the construction of the ISS. The ISS consists of several modules in a variety of sizes. They go up to about 20 metric tonnes. (Ref https://en.wikipedia.org/wiki/Assembly_of_the_International_Space_Station#Assembly sequence.) This is compatible with the size of the Bigelow XBASE, which could form the living quarters of a Moon base.

With fittings and consumables this means we need a launch system that can deliver 25-30 tonnes to the lunar surface. Not even the Block 3 SLS can do that. However the SLS can deliver 25-30 tonne payloads to lunar orbit. The heavy lander, propellant and people would have to be sent on separate launches.

A lunar spacestation makes a good assembly point for the payload, lander, propellant and astronauts. The stations arms will simplify docking them together. The launches can be scheduled over several weeks. With mining equipment, ISRU refining equipment and manned rovers several landing will be needed.

Whether a reusable landing or several expendable landers are used is a cost trade that politicians can understand. Launches are expensive.

A lunar base can repair and refuel landers but only when it is full operational. Prior to that the lander(s) would have to be repaired in orbit and fuelled using fuel from the Earth.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0