Viewing a single comment thread. View all comments

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.