Viewing a single comment thread. View all comments

Bensemus t1_j69pjqv wrote

Human rating the Falcon Heavy and upgrading the Dragon capsule wouldn’t have cost close to $100 billion.


Correct_Inspection25 t1_j69rqqv wrote

You may have misunderstood why SpaceX abandoned the Falcon heavy upgrade to the BFR. SLS is Rad hardened certified can get 59,000 pounds to Lunar orbit, well in excess of the SpaceX Falcon Heavy in full disposable mode to fast LTI Lunar Orbit by roughly 3x. SpaceX dragon is human rated only for LEO and is not rad hardened for operation beyond the van Allen belts due to huge savings in R&D test facilities, time, and costs. This is why SpaceX has been spending 7 years and billions on Starship and the Raptor program instead of BFR/Falcon Heavy tech.


Kellymcdonald78 t1_j69utue wrote

SLS isn’t rad hardened. The only part that even leaves LEO is the ICPS and that’s just taken from the Delta III.

Falcon Heavy in expendable mode has a TLI of about 20,000kg, SLS block I is about 27,000kg hardly 3 times.

Orion does have improved rad hardening, but Dragon solves that issue with multiple redundant systems to compensate for radiation induced bit errors. The same approach being used on Starship


Correct_Inspection25 t1_j6acuza wrote

SpaceX and Wikipedia’s fact sheets would disagree with you. In fully disposable mode, Falcon Heavy can only get 26,000kg to Geosync orbit max, and much less to fast TLI. [NASA approached SpaceX for Falcon Heavy as an option in 2018, but SpaceX responded that slow cargo LTI would be 16,000, and maxed out at 18,000 for the theoretical max for the platform]. The block 1 27,000kg to TLI is like this month’s Starship test, no 100 ton test load to LEO, just an empty capsule with sensors and minimal load for proof of basic delievery and systems integration.)

SLS’s Artemis is rad hardened according to NASA and their results from their test mission.

SpaceX and other commercial crewed vehicles for short LEO mission are allowed to be exempted from Rad hardening using the redundancy you mentioned. Starship HLS will be Rad Hardened based on SpaceX’s latest submission to NASA, and will also use the Water and Fuel tanks in the lander for part of their Rad Hardening solution.


Kellymcdonald78 t1_j6advot wrote

And 16,800 to TMI (Trans Mars Injection). Folks who’ve done the delta V analysis puts the Falcon Heavy TLI performance at approximately 20,000kg

There is no part of SLS that enters into a “high rad” environment except the second stage and for Block I it’s a stage they’ve taken from Delta III. Please let me know exactly what is “rad hardened” on SLS

As well, system redundancy is the exact same method used on Starship, both as part of the Artemis program (as the lunar lander) and potential Mars missions. Crew Dragons are kept on ISS for months, they aren’t exactly “short duration missions”


Correct_Inspection25 t1_j6aivu4 wrote

When approached by NASA in 2018 for potential SLS replacement, they stated to NASA and press questions that the best theoretical max for Falcon Heavy disposable TLI payload is 18,000kg, but only a realistic 16,000kg to lunar orbit for a crewed vehicle. The Mars injection is using the 6 month Holmann transfer window, and remember with crewed missions food/air consumption combined with minimum rad exposure is really important. This means flashlight style month long journeys to lunar orbit doesn’t make sense, and transits need to be between 3-4 days.


Kellymcdonald78 t1_j6aw1is wrote

Falcon 9 performance has continued to improve since 2018. However, let’s go with the 16,000kg number, SLS block 1 still doesn’t have 3 times the payload to TLI, it doesn’t even have twice the payload. We’ll likely get block IB, but it’s unclear if block 2 will ever get funded.


Correct_Inspection25 t1_j6b0yzy wrote

I was using the current SpaceX Falcon Heavy sales spec sheet, and given the amounts to LEO, GEO and Holman Mars transfer window kg hasnt changed from the April 2017 SpaceX website to today, it kinda follows. Now the turn around time per booster reuse has improved markedly with the newer blocks, but the fully disposable mode kg to optimal falcon apogee has not changed since they shifted focus to starship in the beginning of 2018. SpaceX abandoned the falcon platform improvements for the next Gen starship in 2018. If you can show me where on SpaceX’s site or elsewhere the fully disposable kg to LEO/GEO/solar/mars has changed since April 2017, I would be interested why SpaceX hasn’t updated the Falcon Heavy website but gladly concede your point that Falcon could deliver 26,000kg in 3-4 days to TLI.


Kellymcdonald78 t1_j6b60vw wrote

As mentioned folks have done the delta V analysis of the published GEO and TMI numbers and come to the 20,000kg value, but let’s say your 16,000kg number is correct. SLS Block 1 is 27,000kg TLI, so not even twice that of Falcon Heavy.


Correct_Inspection25 t1_j6b8vzu wrote

Who are “folks” and why isn’t SpaceX updating their sales specs to show these performance upgrades to their customers? Updating’s falcon Heavy page costs them nothing and the folks could update the Falcon Heavy wiki if they don’t have access to SpaceX’s webpage.

Want to add SpaceX stated with their last Falcon Heavy performance upgrade, 16,000kg TLI was the high end without much more significant Falcon Heavy R&D/investment/changes to get to 18,000kg TLI that were never studied or developed. SLS Block I 26,000kg to TLI perf isn’t intended to be used beyond Artemis II/III, and 1B will be 42,000 kg to TLI , so more than 2x compared to the max SpaceX said they could do with the most efficient planned production block then and now. SpaceX Falcon Heavy was optimized for different mission use cases than the SLS, and SpaceX told NASA and the press that publicly. That said SLS program will likely be the end of an era for non-interplanetary crewed missions, and private space flight by 2025/2030 will replace NASA except for cutting edge research/deep space missions like new nuclear drives and unproven engine designs too risky for private companies.


Kellymcdonald78 t1_j6bd8ed wrote

SpaceX doesn’t currently publish their TLI payload so I’m not sure what you want them to “update”

Plus the SLS Block IB won’t even fly until 2027 (at the earliest) and that will be the crew version which has a lower payload of 38,000 kg to TLI. So while that version will be more than twice the payload of Falcon Heavy (using your numbers), it will be competing against Starship and Superheavy by then


Correct_Inspection25 t1_j6beblk wrote

Yeah I am not talking about including what food/water/re-entry/life support systems/cargo load for 8-10 days with crew of 4 in a red dragon would be, as SpaceX never produced anything except really rough mock-ups and no test vehicle specs.

I am comparing gross SLS block performance to gross falcon heavy performance to fast TLI (not month long one way insertion). SpaceX has told publications and NASA what the TLI would be. I would say trust SpaceX over some random stack exchange or Quora post (which are the only people I can find referring to your numbers).


Kellymcdonald78 t1_j6bh5ms wrote

As I said, let’s assume your numbers are correct. 16,000kg for TLI for Falcon Heavy. SLS Block I is 28,000kg TLI. That IS NOT 2-3 times the performance of Falcon Heavy. (Twice is 32,000kg which is greater than 28,000kg).

However if you’re going to start comparing what the hypothetical future SLS performance might be in 4-5 years, then expect to compare it against what the hypothetical future SpaceX performance might be in 4-5 years which will be Starship and Superheavy. Falcon Heavy likely won’t even be flying by 2027


Correct_Inspection25 t1_j6bi9ep wrote

Hypothetical also applies to starship HLS and its in orbit refueling, and at least one orbital HLS tanker.

I think they will do it, SpaceX and SLS, just saying we know SpaceX stopped investing in Falcon heavy performance because the math didn’t work for non-LEO missions in 2018. Falcon Heavy BFR is more hypothetical than a vehicle and 80-90% (may be more like 98% as the biggest changes to 1B is just more main tank and SRB fuel capacity segments) of its components that just launched on SLS that will be reused for the newer blocks, as well as the Starship HLS and tankers prototype testing in Texas hopefully kicking off next month. Though the first lunar orbital flight TBD, but hopefully when you suggest, but if we adjust for SpaceX delivery estimation historically 2027-2028 worst case for a crewed NASA lunar mission.)


Kellymcdonald78 t1_j6bjvpz wrote

Yes, I said hypothetical to both. Either you compare the vehicles that are flying today or you compare hypothetical vehicles from 4-5 years in the future.

In either scenario SLS IS NOT carrying 3 times the payload of its competition.

BTW Block II will have completely new SRBs, a new upper stage and a new version of the RS-25. Hardly “80%-90%” of what was used on Artemis I


Correct_Inspection25 t1_j6blzeq wrote

Okay so 16,000 kg to TLI is equal to 26-27,000kg TLI? I was talking about 2023 block Falcon Heavy, not starship, Vulcan, or New Glenn. I will give you it’s not 3x this month, it is 1.7-1.8x, and 2-3x neighborhood is designed and assembly lines with known manufacturing techniques operating right now and has been fitted to test stands. Falcon Heavy isn’t going to get another block in the next 2-3 years, we know that for sure as of Dec 2018.


Kellymcdonald78 t1_j6bo3x2 wrote

Now you’re creating a strawman. I never claimed that the Falcon Heavy was equivalent to Block I SLS. I disputed your claim that it had 3 times the payload.

RS-25E is a completely new assembly line using new production methods and new engine controllers (as the original RS-25 hasn’t been built in decades)

BOLE (the new SRBs) use completely different casings (composite) and a new propellant mixture.

EUS is net new (but will be introduced for Block IA). Heck the mobile launch platform needed for Block 1A and Block 2 is having substantial issues. The only thing common, is the core tanks and thrust structure


Correct_Inspection25 t1_j6bovrz wrote

Ah I thought you implied Falcon Heavy could do what SLS is doing, my error and I did say 2-3x when right now i am off by 0.3x until the block 1B launches. You are right 2 of the new RS-25s testing today haven’t flown before and use 3D printed parts along with parts that have flown on the Space shuttle, but it’s a little different than saying it doesn’t exist and they are completely hypothetical. Same goes for the SRBs. Two other conversations where folks didn’t understand NASA did try and see if Falcon Heavy could replace the SLS key payload to TLI needs several times, the last in 2018, and SpaceX said no and I may have crossed the threads in my head. Let’s hope HLS and the Starship booster and refueling will meet the SLS 1B on time how ever relatively hypothetical they are right now.


Shrike99 t1_j6bfosq wrote

>When approached by NASA in 2018 for potential SLS replacement, they stated to NASA and press questions that the best theoretical max for Falcon Heavy disposable TLI payload is 18,000kg, but only a realistic 16,000kg to lunar orbit for a crewed vehicl


>The Mars injection is using the 6 month Holmann transfer window,

Even the lowest energy Mars transfer still needs more energy than fast TLI.

A best case Hohmann transfer during an ideal window like the 2033 window would be about 3500m/s. However, the upcoming 2024 window will be more like 4100m/s. On average it tends to be around 3900m/s, so I expect SpaceX's payload figures to be based on something like that.

By comparison, Apollo's fast TLI burns were nominally 10,400fps, or ~3170m/s. Call it 3200m/s. No matter how you cut it, the Mars transfer needs several hundred m/s more delta-v.

It seems very odd that an extra ~700m/s to get from GTO to TLI reduces payload from 26.7 tonnes to 16-18 tonnes, or a whopping 10 tonnes less, yet another ~700m/s to get to TMI results in virtually the same payload.

Even if SpaceX are using the best case Mars transfer, you'd still expect it to be a few tonnes less.


Correct_Inspection25 t1_j6ahg5v wrote

Wait so SLS doesn’t use the Artemis rad hardened crewed vehicle? NASA seemed to indicate the SLS launches Artemis to the moon.

I would re-read the latest SpaceX HLS submission to NASA, it included major changes including rad hardening (including moving tanks of water, supplies and fuel for radiation shielding of humans and key systems).

What orbit does the ISS station occupy? [Hint it’s inside the protection of the Van Allen belts at 240 miles. Max LEO orbit is 1,200 miles in altitude.]


Kellymcdonald78 t1_j6aiipl wrote

You said SLS is rad hardened not Artemis (Artemis isn’t even a vehicle, it’s a programme). Orion is “rad hardened” but except for the second stage, SLS doesn’t even leave LEO.

I’ve read the SpaceX submission. They’ve made a few changes to help reduce crew impact in the event of a CME, but the electronics are not rad hardened (radiation hardened CPUs and memory don’t have the performance SpaceX needs)

You also said that Commercial Crew gets an “exemption” because of they’re “short LEO missions”. Hint: they aren’t short


Correct_Inspection25 t1_j6ap550 wrote

Apologies, I was using short in reference to the maximum amount of time SpaceX allows unused Dragons to be docked in LEO to the iSS for 119 days before risk of radiation wear on systems violates crew safety risk parameters in powered down safety mode. Looks like one dragon’s ( maybe Endeavor?) panels maintained their solar production up until 210 days before failing threshold. Active use for dragon is 10 rated for 10 days in LEO.


CurtisLeow t1_j69v3v4 wrote

NASA is paying to radiation harden Dragon. Dragon will be launching cargo to the Lunar Gateway. source

SpaceX is focusing on Starship because it's a better design. But NASA could have absolutely funded a crew-rated, radiation hardened version of Dragon.


Correct_Inspection25 t1_j69w4tx wrote

And the missing 2-3x of disposable Falcon Heavy mass to LTI? SpaceX could have funded the Rad hardened Dragon 7 years ago without NASA funding if they wanted to, but felt Starship was a better investment given the large expense and missing capabilities NASA required of its vendors.


CurtisLeow t1_j6a0av0 wrote

We are talking about NASA, since this is a thread about NASA's SLS. We're talking about alternatives that NASA could have funded to the SLS. NASA could have paid to human-rate the Falcon Heavy, NASA could have paid to radiation harden Crew Dragon. That would have been a viable alternative to the SLS + Orion, at a far lower cost.

SpaceX absolutely decided to focus on Starship. But it doesn't change that Dragon + Falcon Heavy could have been used as a cheaper alternative to Orion + SLS.


Correct_Inspection25 t1_j6a7zgp wrote

You said the Falcon Heavy was an alternative for SLS and it wasn’t going to work even if NASA dropped everything and paid SpaceX for everything. 7 years ago couldn’t meet basic SLS TLI payload/Delta V in full disposable mode means hasn’t ever been a viable SLS replacement for pounds to TLI, even if they had red dragon rad hardened at the time. Look at what SpaceX estimated the weight of Red Dragon, Falcon heavy couldn’t have delivered it to TLI fully loaded even for a reduced crew and scope, SpaceX was right to focus on using what they learned from the falcon Heavy’s failures and used the billions of Starship/Raptor NASA money on the next generation of Heavy Lift.


CurtisLeow t1_j6ahiea wrote

At one point the SLS was going to launch the Lunar Gateway, the cargo to the Lunar Gateway, the Europa Clipper, and crewed Lunar flyby missions. The vast majority of those missions have switched, at least partially, to the Falcon Heavy.

You may not like it, but the Falcon Heavy's performance is very comparable to the SLS. It's good enough. The Falcon Heavy can't launch Orion into TLI, but it can launch Dragon into TLI. NASA is already paying SpaceX to launch Dragon into TLI, as I've already pointed out, as I've already linked. So nit-picking over performance to the Moon is a distraction from the reality. The Falcon Heavy has almost entirely replaced the SLS.


Correct_Inspection25 t1_j6ajvw1 wrote

I love the Falcon program and the Merlin’s, but they fell short for economic heavy lift reuse beyond LEO/ and limited apogee GEO kg to orbit/deltaV. Starship and Raptor economics for heavy lift and deep space crewed missions are money better spent than upgrading SpaceX 2010-2012 technology for NASA.

Please provide SpaceX’s claims that the Falcon Heavy could make TLI in 3-4 days fully crewed with 26,000kg? All the articles I can find when asked, SpaceX told NASA and the press in 2018 if they couldn’t replace the SLS/crewed mission scope, and that the fully disposable Falcon Heavy theoretical max payload to TLI was 18,000kg, but without serious modifications, 16,000kg for crewed 3-4 day TLI transit.

Fun fact: This is shortly before SpaceX publicly completely abandoned upgrading the Falcon Heavy (BFR/Red Dragon) program, and announced the new starship architecture and Booster heavy lift program keeping only the Raptor engines in the late fall early winter of 2018.


Ukulele_Maestro t1_j6crnli wrote

Nothing has stopped SpaceX from doing so. It's a private company after all.