Author Topic: SpaceX Dragon XL  (Read 236276 times)

Offline Karloss12

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Re: SpaceX Dragon XL
« Reply #220 on: 03/29/2020 11:29 pm »
Government procurement guidelines don't allow for predatory pricing, and SpaceX is not known for predatory pricing, so if NASA required the fully capabilities of a Falcon Heavy they would pay $150M for the basic launch service. And if they needed more than the basic launch service, which they normally do, then that would be an added cost, but the basic launch service cost does not change.

True, but there is a surcharge on top of the $150M for the additional insight, documentation and processing controls that NASA insists on for missions of this type (see price differential between F9 launches for commercial vs F9 launches for NASA and USAF (soon to be USSF) missions).

I wouldn't call it a "surcharge". NASA buys additional services for their missions, just like you may buy additional features for the car you buy. That doesn't change the base cost of the product or service.

So in order to make apples-to-apples comparisons the norm is to ignore additional services, and stick with the cost for a basic launch. Especially since what NASA asks for on each mission launch is different, so there is no way to estimate what amount of additional services they will want, or how much the provider the charge. So that just confuses things.

So for purposes of comparison, an expendable Falcon Heavy is $150M.

The cost of developing a new cargo capsule based on legacy equipment is very subjective.
I estimate that the bid price was calculated by offering $150mil for the launch and estimated the costs of the extra's by holding a finger in the air and due to the direction of the wind on that particular day, they plucked out of the air $750mil per launch.
Well, that is how old space priced their orders when they had a monopoly and NASA just had to pay.  Can anyone cite a reason why SpaceX would be any different?  They have a lot of ambitious R&D projects to fund.

Offline Comga

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Re: SpaceX Dragon XL
« Reply #221 on: 03/29/2020 11:54 pm »
Even though the hardware is largely derived from legacy equipment, the Earth-Lunar transfer and docking technology will be an important boost for SpaceX experience.
And SpaceX will be making an absolute packet in profit margins for each mission as they know that they are only competing with the astronomically priced Delta IV Heavy.
This is going to be a much celebrated mission for SpaceX.  They will pocket a lot of cash and also develop themselves a new technology.

My bolding
Can you site evidence of anyone making a killing on a NASA contract?
Even Boeing isn't "cleaning up" on SLS.  They are just getting fixed or award fees for the last decade, and that's good enough.
The company I work for has done a many instruments and missions for NASA.  It's a good business.  Higher margin than the commodity stuff.  But it doesn't bloat the bottom line.
A big issue for SpaceX is that this is seems to be a fixed price contract, IDIQ, for a system involved with astronauts, and at any time NASA can increase the requirements.  SpaceX has experience with this, and probably didn't underbid the competition by $1.6B again. 
But it remains a risk, not a bonanza.
I site the laws of capitalism.  In particular, competition.
The FH costs about $120mil.  The Delta IV is $400mil.
SpaceX will have bid around $350mil and be making a packet.  Good on them.  They need the cash to fund R&D.
One of the great things about NSF is people posting can have good to great knowledge of the engineering or industry.
Just because it doesn’t agree with your intuition is no reason to ignore a post with better background. Mine is not authoritative, but if none of the real experts reading this thread dispute my post, which has happened for others, restating your guess isn’t helping anyone else.
I share your hope that Dragon XL generates some of the profits SpaceX needs to fund their amazing ambitions, but it won’t be a big fraction. It doesn’t work that way.
Edit: Your concept  of how Aerospace contracts are overpriced is interesting but not at all accurate. While some aerospace companies are rapacious, it’s much more sophisticated than pulling prices out of the air. We are all aggrieved by it, but snarling inaccuracies doesn’t help anyone fix anything.
« Last Edit: 03/30/2020 12:02 am by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline testguy

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Re: SpaceX Dragon XL
« Reply #222 on: 03/30/2020 12:07 am »
Government procurement guidelines don't allow for predatory pricing, and SpaceX is not known for predatory pricing, so if NASA required the fully capabilities of a Falcon Heavy they would pay $150M for the basic launch service. And if they needed more than the basic launch service, which they normally do, then that would be an added cost, but the basic launch service cost does not change.

True, but there is a surcharge on top of the $150M for the additional insight, documentation and processing controls that NASA insists on for missions of this type (see price differential between F9 launches for commercial vs F9 launches for NASA and USAF (soon to be USSF) missions).

I wouldn't call it a "surcharge". NASA buys additional services for their missions, just like you may buy additional features for the car you buy. That doesn't change the base cost of the product or service.

So in order to make apples-to-apples comparisons the norm is to ignore additional services, and stick with the cost for a basic launch. Especially since what NASA asks for on each mission launch is different, so there is no way to estimate what amount of additional services they will want, or how much the provider the charge. So that just confuses things.

So for purposes of comparison, an expendable Falcon Heavy is $150M.

The cost of developing a new cargo capsule based on legacy equipment is very subjective.
I estimate that the bid price was calculated by offering $150mil for the launch and estimated the costs of the extra's by holding a finger in the air and due to the direction of the wind on that particular day, they plucked out of the air $750mil per launch.
Well, that is how old space priced their orders when they had a monopoly and NASA just had to pay.  Can anyone cite a reason why SpaceX would be any different?  They have a lot of ambitious R&D projects to fund.
Wow.  All management proposal reviews that I was involved with required extensive cost justification prior to submitting.  Companies need to understand what their exposure is before signing any fixed price contract.  The same is true for cost plus fixed fee contracts because their fee may disappear with cost overruns.  Not only that, poor financial execution could effect the win probability for future proposals.  The government can also perform a fact finding investigation for a bid where the contractor must justify the basis of their bid.  I just have never seen a finger in the air being the basis of a bid.

Offline Asteroza

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Re: SpaceX Dragon XL
« Reply #223 on: 03/30/2020 12:48 am »
Switching to a HTV-X style frunk configuration makes good use of wasted upper frustrum space in the allowed payload envelope of a fairing, but something more significant occurred to me.

Doesn't DXL functionally have the capability to deliver whole modules, in the same vein as multistart upper stages? If the pressurized volume is shortened to the minimum, and a payload adapter fitted onto the frunk/solar array assembly pancake, you essentially have an OTV. Paired with the alleged Class C fairing, that is a substantial volume available to deliver whole modules to ISS or elsewhere. Imagine DXL with a module payload rolling up to ISS, and getting berthed to an IDSS, then the station arm pulls off the module for attachment elsewhere. The minimum pressurized area can be used to offload garbage.

Offline edkyle99

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Re: SpaceX Dragon XL
« Reply #224 on: 03/30/2020 01:26 am »
Quote

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  The only other mode offered on the SpaceX web site and on the NASA NLS 2 mode description is fully expendable.  Just look at the first Block 5 Falcon Heavy result.  6,465 kg Arabsat 6A to a 327 x 89,815 x 22.96 degree supersynchronous orbit.  It all lines up, and has for awhile now.

 - Ed Kyle
« Last Edit: 03/30/2020 01:26 am by edkyle99 »

Offline Coastal Ron

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Re: SpaceX Dragon XL
« Reply #225 on: 03/30/2020 01:34 am »
So for purposes of comparison, an expendable Falcon Heavy is $150M.
The cost of developing a new cargo capsule based on legacy equipment is very subjective.

Not to the engineers that built the legacy equipment. They know their costs, and the potential add-ons for the new design.

Quote
I estimate that the bid price was calculated by offering $150mil for the launch and estimated the costs of the extra's by holding a finger in the air and due to the direction of the wind on that particular day, they plucked out of the air $750mil per launch.

We all have our different ways of gauging things...

Quote
Well, that is how old space priced their orders when they had a monopoly and NASA just had to pay.  Can anyone cite a reason why SpaceX would be any different?  They have a lot of ambitious R&D projects to fund.

I've worked for government contractors, as have some others that have commented here. While there are creative ways to boost the profitability of government contracts, that normally doesn't happen on the scale you are talking about. And especially for Fixed Price contracts, contractors are very careful in how they do their estimating.

One company I worked for had a "Tiger Team" that reviewed all bids, and the team was made up of people from outside of our division in order to ensure no bias. Their job was to make sure the company did not lose money on the contract being bid.

And the government does have the ability to audit bids to ensure that contractors are not being unreasonable with their pricing.

There are ways to beat the system though. The SLS and Orion contracts were pretty much given to Boeing and Lockheed Martin by Congress, and NASA had no choice at first but to use Cost Plus contracts, since the designs were owned by the government but needed to be created by contractors. It has been a horrible situation for the taxpayer, but it has succeeded in the eyes of the politicians (and Boeing and Lockheed Martin).

Most contracts don't allow this type of situation though, and Gateway Logistics Services contract is one of those due to the way it was bid.

My $0.02
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Online Robotbeat

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Re: SpaceX Dragon XL
« Reply #226 on: 03/30/2020 01:43 am »
Quote

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  The only other mode offered on the SpaceX web site and on the NASA NLS 2 mode description is fully expendable.  Just look at the first Block 5 Falcon Heavy result.  6,465 kg Arabsat 6A to a 327 x 89,815 x 22.96 degree supersynchronous orbit.  It all lines up, and has for awhile now.

 - Ed Kyle
No; that doesnít line up with 16.7tons to Mars. Either the Mars figure is too optimistic or 8 tons GTO is too pessimistic.

Regardless, itís false to say ďcomes directly from SpaceX.Ē
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline GWH

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Re: SpaceX Dragon XL
« Reply #227 on: 03/30/2020 01:54 am »
Switching to a HTV-X style frunk configuration makes good use of wasted upper frustrum space in the allowed payload envelope of a fairing, but something more significant occurred to me.

Doesn't DXL functionally have the capability to deliver whole modules, in the same vein as multistart upper stages? If the pressurized volume is shortened to the minimum, and a payload adapter fitted onto the frunk/solar array assembly pancake, you essentially have an OTV. Paired with the alleged Class C fairing, that is a substantial volume available to deliver whole modules to ISS or elsewhere. Imagine DXL with a module payload rolling up to ISS, and getting berthed to an IDSS, then the station arm pulls off the module for attachment elsewhere. The minimum pressurized area can be used to offload garbage.

This is an important feature to note. Not just ISS but also Gateway should SpaceX choose to offer delivery services for additional modules.

Offline Nathan2go

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Re: SpaceX Dragon XL
« Reply #228 on: 03/30/2020 02:35 am »
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  ...
No; that doesn’t line up with 16.7tons to Mars. Either the Mars figure is too optimistic or 8 tons GTO is too pessimistic.
...
Ah, perhaps you're thinking of the old statement that reusing an F9 booster causes a penalty of about 15% for downrange recovery and 30% for RTLS?

Don't forget that Falcon Heavy has an additional problem:  the 2nd stage did not triple in mass when the first stage tripled.  To get good staging efficiency in a multi-stage rocket, for each staging event, you want the part of the rocket that continues forward to be massive compared to the part the returns to Earth.  For FH that 2nd stage is pretty light compared to a set of boosters loaded for retro-braking and landing; that makes the performance with full booster re-use much less than triple that of the F9.

For this reason, I think that if SpaceX were willing to invest more in the FH (i.e. if they were not confident in Starship), they would have done a tank stretch for the upper stage.  They would not get back all of the reduction without adding more thrust too, but a stretch would help.

By the way, I don't have a hard number, but the booster RTLS penalty for Superheavy should be well under 30%:  the 2nd stage is proportionately more massive, so it naturally wants to have stage separation closer to the launch site (in distance and velocity).  Also, the Raptors have better Isp. 
« Last Edit: 03/30/2020 02:52 am by Nathan2go »

Offline baldusi

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Re: SpaceX Dragon XL
« Reply #229 on: 03/30/2020 03:01 am »
Quote

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  The only other mode offered on the SpaceX web site and on the NASA NLS 2 mode description is fully expendable.  Just look at the first Block 5 Falcon Heavy result.  6,465 kg Arabsat 6A to a 327 x 89,815 x 22.96 degree supersynchronous orbit.  It all lines up, and has for awhile now.

 - Ed Kyle

Use NLS II performance estimator. I used a c3=-0.5. FHR = 6.7tonnes, FHE gets 15.1tonne. I personally think the TMI number they post is utter bollocks.

Offline russianhalo117

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Re: SpaceX Dragon XL
« Reply #230 on: 03/30/2020 03:23 am »
Quote

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  The only other mode offered on the SpaceX web site and on the NASA NLS 2 mode description is fully expendable.  Just look at the first Block 5 Falcon Heavy result.  6,465 kg Arabsat 6A to a 327 x 89,815 x 22.96 degree supersynchronous orbit.  It all lines up, and has for awhile now.

 - Ed Kyle

Use NLS II performance estimator. I used a c3=-0.5. FHR = 6.7tonnes, FHE gets 15.1tonne. I personally think the TMI number they post is utter bollocks.
Elon did post that there is a discrepancy in the calculator that is being fixed.

Offline TheRadicalModerate

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Re: SpaceX Dragon XL
« Reply #231 on: 03/30/2020 04:40 am »
Switching to a HTV-X style frunk configuration makes good use of wasted upper frustrum space in the allowed payload envelope of a fairing, but something more significant occurred to me.

Doesn't DXL functionally have the capability to deliver whole modules, in the same vein as multistart upper stages? If the pressurized volume is shortened to the minimum, and a payload adapter fitted onto the frunk/solar array assembly pancake, you essentially have an OTV. Paired with the alleged Class C fairing, that is a substantial volume available to deliver whole modules to ISS or elsewhere. Imagine DXL with a module payload rolling up to ISS, and getting berthed to an IDSS, then the station arm pulls off the module for attachment elsewhere. The minimum pressurized area can be used to offload garbage.

I doubt they'll be anywhere close to going into the frustum.  You don't just make this thing longer for the fun of it--extra length is extra dry mass.  It's not a hab module, it's not some structural component for future work; it's a pressurized cargo system.  Even if you figure 4 m of length for prop, consumables, and frunk (which is way more than is needed), that gives you at least 2.7 m of cargo length in the cylindrical portion of the fairing.  At 3.7 m diameter, that's 29 m≥.  For comparison, Cygnus is 18 m≥.

Or you can work backwards:  I can see SpaceX wanting to exceed the RFP specs and go for maybe 8 t of cargo instead of 5 t.  CRS-2 specs specified a cargo density of 290 kg/m≥ (see [url=https://oig.nasa.gov/docs/IG-18-016.pdf, p. 16), and I can't see that the Gateway would require anything less than that.  So 5 t would be 17 m≥, and even 8 t would be only 28 m≥.  Those are 1.6 m and 2.6 m of length, respectively.  That leaves a minimum of 4.1m for the frunk.

As for delivering modules:  If NASA wants to launch modules to the Gateway, they'll put 'em in a fairing and launch 'em on commercial platforms.  No need for DXL to do that.

That said, I do think it's possible that you'll see some way of carrying MMH and NTO in the frunk, because I think NASA's planning on refueling at least the HLS ascender using something like this, and possibly part of the lander as well.  That could happen even before the Gateway is deployed; it kinda depends on how quickly they want to go for reuse of the ascender.  But given that they have to launch 2 SLSes for each lunar surface mission before ascender reuse, I'm guessing it's gonna be pretty early in the program.  A decent-sized ascender needs 5 tonnes of MMH/NTO, which is about 4.3 m≥.

Offline TheRadicalModerate

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Re: SpaceX Dragon XL
« Reply #232 on: 03/30/2020 04:44 am »
Use NLS II performance estimator. I used a c3=-0.5. FHR = 6.7tonnes, FHE gets 15.1tonne. I personally think the TMI number they post is utter bollocks.

TLI C3 is usually about -2.  Even for the BLT orbits, it's less than -1.6.

Offline woods170

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Re: SpaceX Dragon XL
« Reply #233 on: 03/30/2020 07:31 am »
I'm guessing these have to be fully expendable Falcon Heavy launches, to get 5 tonnes of cargo to lunar orbit in a spacecraft that has to weigh 5-times-something tonnes - maybe 20 tonnes at TLI with about 1/4th of that mass needed for lunar orbit insertion.

 - Ed Kyle

Can't give you the exact numbers but my source says your mass estimate for the vehicle is way off. As in: your mass estimate for the vehicle is way too high.
Is your source counting the mass needed for lunar orbit insertion?  Maybe there is an entirely separate stage, or maybe the Falcon upper stage does some of the work.  Consider this example.  Apollo 17 entered trans-lunar injection at 46.8 tonnes.  After its lunar insertion burn, the CSM/LM combination weighed 34.72 tonnes, using 26% of the TLI mass for that maneuver. 

So, if payload is 5 metric tons (tonnes)(SpaceX number), then the spacecraft plus payload in lunar orbit has to weigh maybe 2.1 to 2.75 times as much (see Cygnus, ATV, HTV, etc), which gets us to 10.5 to 13.75 tonnes.  That mass divided by 0.74 for the lunar insertion gives 14.2 to 18.6 tonnes at trans-lunar injection. 

Of course this assumes a low lunar orbit delta-v maneuver, which I guess isn't happening in this case.  From TLI to the Gateway NRHO using a lunar flyby would be something like 420 m/s delta-v, which for a 300 sec ISP Draco assumption would I think require about 13.5% of total TLI mass for the burns, resulting in a 12 to 15.9 tonne TLI mass range.

This seems to me to be in the range requiring an expendable Falcon Heavy based on published and proven capabilities.  SpaceX may be able to do downrange side booster recovery and achieve this result (while expending the center core), or some of it, but downrange recovery of two cores simultaneously on a Heavy flight has yet to be demonstrated.

 - Ed Kyle 

Your mass estimates in your second-to-last paragraph are much more like it according to my sources.
And they are also beginning to match with this NASA requirement:

Quote from: Attachment_03,_GLS-RQMT-001_Gateway_Logistics_Services_Requirements
L3-GLS-1106 Maximum System Docking Mass
Upon first docking to Gateway, the Logistics Module mass, inclusive of cargo and payloads, shall not exceed 14 metric tons (30,865lb).
« Last Edit: 03/30/2020 09:25 am by woods170 »

Offline woods170

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Re: SpaceX Dragon XL
« Reply #234 on: 03/30/2020 07:35 am »
Would Dragon XL require the future elongated FH fairing?
I'd assume that (like current Dragon), it is its own fairing, likely with a larger jettisoned nose cap a la Dragon 1.

Then why are the control thrusters sticking outside the trunk? Perhaps this is just a rough render for now but strange the RCS thrusters are not placed inside wether or not it uses a fairing.

That was early speculation, we now know that it will be in a regular FH fairing. See Woods170's post above.

Was also confirmed publically by a NASA official:

https://spaceflightnow.com/2020/03/27/nasa-picks-spacex-to-deliver-cargo-to-gateway-station-in-lunar-orbit/

Quote from: Stephen Clark
Unlike the Dragon 2, which flies without an aerodynamic shroud on top of SpaceXís Falcon 9 rocket, the Dragon XL will lift off inside a payload fairing on the companyís bigger Falcon Heavy launcher, according to Dan Hartman, NASAís Gateway program manager at the Johnson Space Center in Houston.

Offline woods170

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Re: SpaceX Dragon XL
« Reply #235 on: 03/30/2020 08:03 am »
People are trying to project their hopes and dreams onto this thing, but it's just an expendable Dragon 1 variant with a non-tapered "capsule" to fit more cargo.

Spot on. Well done. Except that it is a Cargo Dragon 2 variant. Not Dragon 1.

This isn't going to have an aft docking adapter. It's not going to be recyclable as a station module. It's not going to launch inside a reusable payload fairing. The only reusability potential in this concept is the FH boosters.

Emphasis mine.

It IS going to be launched inside a fairing: https://spaceflightnow.com/2020/03/27/nasa-picks-spacex-to-deliver-cargo-to-gateway-station-in-lunar-orbit/
Quote from: Stephen Clark
Unlike the Dragon 2, which flies without an aerodynamic shroud on top of SpaceXís Falcon 9 rocket, the Dragon XL will lift off inside a payload fairing on the companyís bigger Falcon Heavy launcher, according to Dan Hartman, NASAís Gateway program manager at the Johnson Space Center in Houston.

If the Gateway comes to fruition, this is a relatively low-cost design evolution for cargo supply. This isn't something that SpaceX would have wanted on their roadmap, and I doubt they anticipate any commercial market for a vehicle like this, but it would have been poor form for SpaceX not to bid. SpaceX has a strategic interest in playing nice with NASA, and while developing Dragon XL would be a distraction, it's not an overly burdensome detour. NASA will pay enough to make it worthwhile for SpaceX even if they're the only conceivable customer.

This is indeed a relatively low-cost design evolution.
BUT
This is very much something that SpaceX is very willing to build and fly for NASA. Reason: SpaceX needs every dollar it can get to finance the development of Starship and Superheavy. Not just now, but also 10 years from now because, like FH and F9, Starship and Superheavy will be in near-constant development & improvement for at least a decade to come.

People will need to drop the idea that SpaceX will stop doing NASA-specific work once Starship and Superheavy start flying. That is not going to happen. Going to Mars is going to be expensive for SpaceX. Granted, it will not nearly be expensive as the NASA way, but still, it is going to be expensive.
Elon Musk is very much aware of this. That's why he has broadened the scope of income for SpaceX. Launching stuff for government agencies (such as NASA) is one source of income. Another is launching stuff for private companies (for example comsats). A third is providing broadband internet from orbit (Starlink). And SpaceX is actively working on a few more ideas to generate revenue and profit. All these efforts are done to support the development of Starship and Superheavy. As such, Dragon XL is a project SpaceX is willing to do. It is already actively being worked on. Early development is in progress. This is not just a pretty powerpoint. Design- and development engineers at SpaceX are already actively working on Dragon XL.

Also: SpaceX has no problem with building something that has just one customer (NASA in this case). They did the same when building Dragon 1 and Falcon 9 v1.0. Also, the MST for LC-39A will also have only one customer: USAF. The only condition is that said customer fully pays for the required service and hardware. And that is exactly what NASA will do for Dragon XL. The full financial burden for Dragon XL development will rest on NASA.

Maybe (hopefully?) SpaceX won't ever actually have to build one of these. They'll work through the paper milestones and continue to strengthen their relationship with NASA, because that relationship is what will endure the ever-changing roadmaps for human exploration.

Emphasis mine.
As long as Gateway exists as an official NASA program SpaceX will build this thing.
« Last Edit: 03/30/2020 08:04 am by woods170 »

Offline Asteroza

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Re: SpaceX Dragon XL
« Reply #236 on: 03/30/2020 08:20 am »
Switching to a HTV-X style frunk configuration makes good use of wasted upper frustrum space in the allowed payload envelope of a fairing, but something more significant occurred to me.

Doesn't DXL functionally have the capability to deliver whole modules, in the same vein as multistart upper stages? If the pressurized volume is shortened to the minimum, and a payload adapter fitted onto the frunk/solar array assembly pancake, you essentially have an OTV. Paired with the alleged Class C fairing, that is a substantial volume available to deliver whole modules to ISS or elsewhere. Imagine DXL with a module payload rolling up to ISS, and getting berthed to an IDSS, then the station arm pulls off the module for attachment elsewhere. The minimum pressurized area can be used to offload garbage.

This is an important feature to note. Not just ISS but also Gateway should SpaceX choose to offer delivery services for additional modules.

Functionally not that different from the hacked up Progress that were used for delivering some ISS russian modules, correct? Or am I misremembering that?

Though as TheRadicalModerate points out, the existing fairing gives a lot of frunk headroom as is for normal frunk work. Whether a DXL based OTV for module delivery to LEO, using the Class C fairing, makes any sense is up for debate, and gateway modules being delivered by others would suggest no need for gateway modules to be hauled by a DXL derivative per se. But the pieces for LEO module delivery ostensibly fall into place, the only real US long duration precision delivery with berthing competitor at present being a cut down Cygnus.


Offline woods170

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Re: SpaceX Dragon XL
« Reply #237 on: 03/30/2020 08:45 am »
This brings up a question I've wondered about a bit.

This is cargo.  It's not necessarily 'speed sensitive' on delivery.  Therefore, would it not be a reasonable consideration to increase cargo mass by going with a different proven thruster technology. Say an Ion Thruster something like DS-1 used?  Trading fuel mass for cargo mass?  So it takes weeks instead of days to arrive.  Again, it's not necessarily time critical on the delivery.

The Falcon Heavy second stage provides the thrust to deliver the Dragon XL to its destination. The maneuvering thrusters on the Dragon don't contribute to the time to the destination except to maneuver to the berthing portal at the Gateway. Or to the target location if the mission is prior to the Gateway's existence. In any case, there isn't any suitable application for Ion Thrusters.

And by the way, so far we have discussed the issue of disposal of the Dragon XL after the mission is complete, but I don't recall anyone mentioning the ultimate destination of the Falcon Heavy stage 2. It will be in the general vicinity, too. Isn't the Gateway at L1? Or is it L2? Will stage 2 hang around the Gateway for any unreasonable time? It should still have some maneuvering capability, could any use be made of this spent stage?

If the FH needs more total impulse to send the payload to Gateway, then the option of streching the stage 2 tanks is on the table.

We haven't seen any evidence that the FH second stage will do the TLI burn.  To the contrary, the only thing we've seen said the spacecraft would be released in High Earth Orbit, which would mean the Draco thrusters would be used to get to Gateway from Earth orbit.  This type of mission could be done with electric propulsion, but the vehicle would need more electrical power.

Emphasis mine.

You seem to be forgetting that launching into an initial Earth orbit with an apogee of 1.5 million kilometers, and a perigee of 60,000 kilometers is the very definition of "High Earth orbit".

What I hear from my sources is that Dragon XL is going to be launched towards Gateway's NRHO the same way as the logistics module and lander elements: Ballistic Lunar Transfer. Which basically means: no TLI required. Transfer time before capture in the NRHO is 12 to 20 weeks.

Stop thinking Apollo-style 3-day transfers. This is a cargo shipment. It doesn't have to arrive at the Gateway in under a week.
« Last Edit: 03/30/2020 08:47 am by woods170 »

Offline woods170

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Re: SpaceX Dragon XL
« Reply #238 on: 03/30/2020 08:55 am »
Quote

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.
All evidence points to 8 tonnes being for flyback boosters and downrange core recovery.  The only other mode offered on the SpaceX web site and on the NASA NLS 2 mode description is fully expendable.  Just look at the first Block 5 Falcon Heavy result.  6,465 kg Arabsat 6A to a 327 x 89,815 x 22.96 degree supersynchronous orbit.  It all lines up, and has for awhile now.

 - Ed Kyle

Ah, I see you are making the classic Ed Kyle mistake again. That is: not believing the max. performance figures of a launch vehicle until that launch vehicle has - in fact - launched that max. mass to orbit.

We've had this discussion before, and it was cut short by the mods for all the right reasons: your line of reasoning is flawed.

Offline soltasto

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Re: SpaceX Dragon XL
« Reply #239 on: 03/30/2020 09:35 am »
Does anyone have a good estimate for Falcon Heavy near-escape capability for core-expendable and booster down-range recovery mode?  Such a mode does not yet exist, of course, because SpaceX hasn't demonstrated dual downrange recovery.  I know about Elon's 10% payload reduction estimate, but he never said if that was for LEO or GTO, etc.  My guess is 10% for LEO, but a bigger reduction for higher energy orbits. 

My estimate for 5 tonnes cargo to Near Rectilinear Halo (lunar) Orbit (NRHO) is that 12 to 16 tonnes (payload, spacecraft, propellant) would need to separate into TLI, providing 10.5 to 13.8 tonnes to NRHO (13.5% of mass used for the burns to NRHO).  The three-core recovery mode for Falcon Heavy only provides 8 tonnes to GTO, while fully expendable Falcon Heavy is listed at 26.7 tonnes GTO or 16.8 tonnes trans-Mars.

 - Ed Kyle
Citation needed for just 8 tons GTO with 3 booster recovery. I think the assumptions for that are much more conservative (sandbagged) than those for the 16.8tonnes TMI estimate.

Also, center core expended and 2 cores RTLS is a thing.

I think that comes directly from SpaceX:

https://www.spacex.com/about/capabilities
Nope!

Read again! Thatís just the performance you get for $90m; it says nothing about what the mode of launch would be at that price.

Secondaries? RTLS for all 3 cores? Extra margin for a softer recovery? Cheaper/lighter payload adapter? Who knows! It isnít specified!

We do know from that page it can do 26.7t GTO in fully expendable mode.

Maybe an official slide from Spacex presented at Hans Koenigsman's Ted talk at IAC 2018 (you can find the video on youtube too) will be sufficient.
Notice the plus sign on the Expendable Falcon Heavy figure.
All these figures could be outdated, but they are the figures SpaceX gave out officially. I think the figures on their website are estimates with close to no fuel margins, which might be ok for an internal mission or for rocket comparison purposes but not for commercial launches or government launches. The NASA LSP figures could also be very conservative, there is no doubt in that.

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