sevenperforce

Well yes, a Starship tug makes things much easier. My point is that the reason people would want something NOT SpaceX is for redundancy if SpaceX can’t make reusable LEO retanking into a thing. And if they can’t, then we have to figure out how to get stuff to Gateway (and, ultimately, the lunar surface) using repeated expendable commercial launches. Suppose you have an HLS architecture that uses three components, like National Team. Each of those components has to get to Gateway somehow. So either it is launched to TLI by itself and brakes itself into NRHO (and thus has to perform the rest of the mission with partially depleted tanks) or it is launched to TLI with a transfer stage that brakes it into NRHO and is then discarded. It has to be one or the other. It just makes more sense to me to have an oversized transfer stage that brakes all your sortie propellant into NRHO in one launch, then reduces your (minimalist) lander’s dV requirements so it can return from LLO to Gateway on RCS.

It should also be noted that the surface payload delivery scheme involves the exact same architecture but doesn’t require a crasher stage. The resupply stage would be set up the same way but would have the payload mounted between the top of the resupply stage and the bottom of the replacement RCS tank. It would probably use some of its own props to complete TLI (since it would be heavier out of LEO) and expend most of its remaining props braking to NRHO. If you’re dropping something off on the lunar surface that you don’t have to take back to Gateway, the lander can get from Gateway to the lunar surface and back to LLO in a single stage, drop the tanks, and head back to Gateway on RCS.

Well, unless we’re going fully reusable with Starships, then every payload we send to TLI has to have an independent bus with enough propellant (or, if it’s a HLS component, extra propellant) to brake itself into NRHO, which means you have a bunch of derelict buses floating around the Gateway (and the HLS components arrive with tanks already partly depleted). You can deliver HLS components to Gateway with a separate transfer stage, of course, but then you have THAT transfer stage floating around Gateway. If you’re already dumping spent stages in cislunar space, you might as well make them part of the landing architecture. And this architecture drops tanks suborbitally so there’s only one fairly small RCS tank that ends up at Gateway.

Here's an idea. Two vehicles, a lander and a resupply/transfer vehicle. First, the lander. Stick with the eight-engine cluster (redundancy is good) but make them simple pressure-fed hypergolic engines instead of cryogens. Same overall low-slung design. However, there are no integral tanks at all. There are three mounting points for tanks, each with propellant flow couplings and a simple load-bearing locking mechanism: two on the "wings" mounted over the engines, and one directly underneath the capsule. The mounting points on the wings are plumbed to the main engines; the mounting point under the capsule is plumbed to the RCS array. Second, the resupply/transfer vehicle. It will also act as a crasher stage a la N1-Blok D. It can be cryogenic but has its own RCS and power supply. It carries three tanks: the lander RCS tank in the front with the mounting point exposed and the two wing tanks on either side. The wing tanks have a quick release element that allows them to be dropped quickly without needing to remove the entire load-bearing mounting point attachment, and of course the transfer stage also can drop away from the RCS tank quickly. Between missions, the lander is docked to Gateway without tanks. The resupply/transfer stage is launched to TLI on a commercial LV and the efficient cryogenic engine takes it to Gateway, where the station's Canadarm grapples it and attaches it to the base of the lander via the load-bearing mounting point. Once secure, the Canadarm moves the two wing tanks from the sides of the transfer stage onto their respective mounting points. The crew gets in and the vehicle undocks, then performs a checkout to make sure all the propellant is flowing properly to the onboard engines and RCS. Then the transfer/resupply stage takes them from NRHO to LLO and then performs the deorbit burn. It then ignites one remaining time to burn to depletion and scrub as much horizontal velocity as possible. Once the transfer stage is depleted at ~5 km and <200 m/s, it is jettisoned and the lander engines ignite to scrub off the remaining velocity and land. On the surface it do what it do. It's a minimalist design, dependent on pre-emplaced resources. But because it is so low slung you could even drive a pressurized rover right up to it and dock with it, if it had a docking port on the opposite side. At mission conclusion, it's back to orbit. Just before circularization is completed, the tanks are jettisoned. The lander uses its RCS to complete circularization and head back to the Gateway. Upon return to Gateway, Canadarm can be used to carefully remove the RCS tank from its mounting point as well as the stubs remaining on the wing mounting points, and it's ready for the next sortie. Launched to LEO with all three tanks in place, the lander can perform TLI and reach Gateway on its own. If the cabin is removed, the same superstructure and mission profile can be used to reusably deliver payloads to the moon (the transfer stage would carry the lunar surface payload, like a hab or pressurized rover and mount it to the empty lander in the same way, and the lander would have enough dV to take it to the surface and return to Gateway). This is good because there's no need for propellant transfer; the tanks provide pressurization. No need for cryogens (other than the crasher stage). All tanks are disposed of in a controlled way and there is no wasted tank space. And I'm sure the math would close much more easily.

The Source Selection Statement says Dynetics was planning on using cryogens but it's unclear if they were using an existing engine or waiting to design one. If you were in charge at Dynetics and had an opportunity to re-bid and could use any engine, what engine would you pick and what kind of propellant resupply mode would you pick for reuse? Assume Gateway has a Canadarm and can grapple replacement tanks. It would be cool to see something that borrowed a little from the Blok D crasher stage architecture. The Rutherford engine might not be a bad fit.

The Big Dumb Boosters were intended to use simple, low-cost engines with a low part count. There were several attempts at designing such an engine but the ones that got furthest along were the hydrolox TR-106 and the kerolox TR-107. They used an oxygen-rich staged combustion cycle but with lower performance (the TR-107 had only 66% the chamber pressure of an RD-180), allowing it to be easier to build while still being reliable. They used pintle injectors for throttleability and simplicity, and they used an ablative combustion chamber. When they were test-firing it, they found they could simply swap out the ablative combustion chamber liner on the test stand and refire without needing to replace any of the parts because the whole thing was relatively simple. Another Big Dumb Booster engine design was Fastrac, which also used an ablative liner but had a simple single-shaft, dual-impeller turbopump built by Barber Nichols operated by a kerolox gas generator. It used a hypergolic liquid igniter for startup simplicity and also used a pintle injector. Tom Mueller was the project manager for the TR-106 and the TR-107, and the original Merlin 1A turbopump was built by Barber Nichols. The Merlin uses a pintle injector and ever since the Merlin 1B has used hypergolic liquid ignition. The original Merlin 1A also used ablative cooling but it was upgraded to regenerative cooling by the Merlin 1C. And so SpaceX ended up with an engine that could be easily refired and could be repeatedly upgraded to squeeze out more and more performance, enabling the evolution from the original Falcon 9 to the Falcon 9 Block 5.

Good grief the website really does suck. Ugh. Who thought this would be cool? It's not. At 13 meters that's not much bigger than the SS-520-5. Cool that they are using a COTS engine. 5000 pounds-force is a touch over 22 kN so we are looking at roughly the same thrust as a Rutherford. Surprising that they aren't putting a vacuum nozzle on the upper stage but with ORSC they may not need it.

That’s a weird shape for an engine. Looks like kerolox but I can’t be sure.

Humans are mostly water so just run the numbers with water.

I wonder how much he offered her. He probably thought he could just buy her like a trinket......

That was what Musk said at the presser immediately after SES-10, the first successful reflight. A lot of his numbers are off-the-cuff but if he said a billion I doubt it is less. Hardware costs for individual boosters are minimal, yes, and most of the test landings were incidental to commercial flights. But it took a long time to get there. SpaceX had to build facilities at McGregor to allow flight tests there rather than just stand tests. They had to dev and build and operate Grasshopper for eight flights. They had to dev and build and operate F9RDev1 for five flights. They build a Dev2 vehicle and leased space at Las Cruces and built a pad there, but canceled it. They had to do all the modeling and write all the code for hypersonic retropropulsion. They had to buy the barges and retrofit them as droneships and design all the software for autonomous station-keeping. They had to pay the boat people and rent the chase planes. They had to research the legs and design the legs and build the legs and destructively test the legs. They had to come up with the grid fin control hardware and write the software for it. All of that work by people who were getting paid by SpaceX and who weren't contributing to commercial activities. I'm sure it's more than a billion. It's a good thing chute recovery never really took flight (pun intended). Now, Merlin 1D *is* designed to be test-fired and re-test-fired and static fired before launch, like a car engine that can be restarted over and over and over again as long as you change the oil periodically. Not only does that make recovery by propulsive landing possible, but it makes rapid reflight possible. Nothing like the Shuttle program. The Orbiter never brought the RS-25s back; it merely brought the RS-25 parts back. Most non-hypergolic liquid-fueled rocket engines designed through the history of spaceflight could not be readily relit. The J-2 and the RD-58 were some of the first, I believe. I can't remember whether the RL10 could originally be relit or not. They certainly weren't relit when they flew on the original Saturn I S-IV. I know you weren't asking me, but because I often answer when I'm not asked...I think the Raptor engine was harder to design and I think the jet engine is harder to manufacture. Finding a new way to do something that has never been done before is hard.

Wait, are they going to relaunch it after all??!! I had thought SMART was shelved but yesterday Tory said it wasn't, so... Tory also wished my seven-year-old a happy birthday yesterday and did so with cool facts. Elon may send Doge to the moon with his tweets but Tory's Twitter game is way better. That's partly because Centaur SEC has such low dry mass but mostly because the RL10A-4-2 is arguably the best upper-stage engine, ever. It weighs so little that even without the extra specific impulse of the RL10C-2-1 it usually wins. Unfortunately it really only works properly for very small payloads, and it can't be scaled up, and it can't be clustered well since it relies on radiative cooling. Presumably the same geometry that chokes the flow at the nozzle throat serve to stagnate airflow at the throat and thus insulate the chamber. It's just as if it is restarting at a slightly higher ambient pressure than it otherwise would. The equation for the effective elevated air pressure inside the combustion chamber is given by 8ρv2, and once the engine restarts then the equation for the effective air pressure it's pushing against becomes ρv2/2. Borrowing numbers from NROL-108, the entry burn starts with an effective in-chamber air pressure of 5.8 kPa, just 6% of atmospheric pressure at sea level. At the end of the entry burn the engine is pushing against an effective ambient pressure of 4.2 kPa, again a fraction of what it does at sea level. The landing burn restart takes place at around 4.5 km, where the air pressure is already more than half of sea level. The total pressure at the nozzle throat here is the bigger challenge; it's actually about 630 kPa or more than six times the ambient pressure at sea level. But it's less than 7% of the Merlin 1D's actual chamber pressure so it's not a big deal. Raptor hasn't had any issues with retropropulsion. It has had issues with starting up properly while falling sideways due to propellant flow. No way it's 4. 4 could be for a lightly fueled hop. (just SH, nothing on top) I'd think something like 20 SL Raptors is the bare min. Maybe fewer if the fixed ones generate more thrust. Starship Mk1 was 200 tonnes and their goal is to get down to 120 tonnes, so I'm guessing that SN20 will be somewhere in the 140-150 tonne range. Assuming it launches fully loaded with propellant and all six engines (averaging 370 s specific impulse), but no payload at all for the initial orbital test, it will boast an impressive 7.3 km/s of dV. That's a full 1 km/s of dV that Superheavy doesn't have to provide. The actual effective dV of a fully fueled Superheavy with a full Starship on top is around 3.95 km/s, so it should be able to launch with about a 75% propellant load if there is no payload on Starship and Starship provides more of its own boost to orbit. A full stack would typically be just over 5000 tonnes so reducing Superheavy's load by 25% would put the full stack at 4200 tonnes or about 83% of the normal loaded weight. Probably a little bit more, though, since Superheavy will be a touch overweight at this point. So you need 24 Raptors minimum to match the intended TWR of a full stack. The booster engine is tailored for Superheavy, not for Starship. That was just incredible. It looks like they did a three-engine kick but then cut the engine just as rotation was canceled. It also looks like they are now essentially beginning the landing burn during the kick-flip. It boggles my mind how it can come down at an angle like that until just a few meters above the pad and then land upright.

If reusing a stage costs $1M and saves them the ~$18M it costs to build a new stage, and they can reuse stages ten times each, then it would take 66 launches at full commercial price to recover the $1B it cost to develop Falcon 9 first-stage reuse. That's a long time. Instead they're reinvesting that capability by selling themselves Starlink launches. Bingo. More than half of their reflights are going to Starlink (since the F9B5 debut, there have been 26 operational Starlink launches and 22 commercial launches on reflown boosters). So that's more like 80-90 commercial launches to recoup the dev costs. And even if they make that, their investment in upper stages and launch costs for Starlink still has to be recovered.

Agreed

You should see Roscosmos' prediction as well as the prediction made by the last TLE from 18-SPCS/CSpOC (which is later than their last public prediction). Honestly I'm wondering about the SBIRS that the major space nations have when they called it actually re-entering, wouldn't surprise me if all three have it. $%&@#~!

Yep! Looks like it will be clear from 8-9 PM local time too. This launch was originally planned for Saturday night during the Long March 5B fiasco but they had to stand down due to high winds. My kids might even be able to see this from where they are in Virginia.

I will say that US Space Command's prediction of CZ-5B R/B's re-entry point was wildly impressive. The Space Force made its final prediction just before 5 PM EDT on Saturday: re-entry at 10:11 PM EDT plus or minus 60 minutes. At that point in time, Aerospace Corporation still had a four-hour window centered at 11:40 PM EDT, which only had a small overlap with the Space Force window. I was nervous about trusting such a narrow prediction made relatively early. And then...it came down at 10:14 EDT. Literally three minutes later than the prediction. Like, that is GOOD. Really validates our abilities in that area and, to some degree, the whole idea of having a "US Space Command" as an independent entity. Not to get all nationalistic or anything...it's just very impressive. Also, today in poorly-written space headlines: "With no landing pad"?!?! What in the world.

**have been waiting for this** What a lovely sound. They said it couldn't be done. Ten flights for a single booster. Just incredible. Now this makes some sense, yes they could restart at AP, but if under trust they have more control, and yes I get why they don't want to go supersonic. If they cut the engines entirely and tried to coast to apogee at any significant speed, the whole stage would probably start to tumble. Probably end up inverted with the heavy engines pointing skyward.

It would take more than just retrorockets. If you look up the design report for the YF-77, the integrated IMU loop and control unit is routed directly to the engine gimbal and nothing else. There is no AOCS at all. The observed high rotation rate of the boosters means that there was a significant amount of undamped torque on the rocket body at staging and during engine shutdown/outgassing and tank passivation. Without a functioning AOCS and cold-gas thrusters to control attitude, the retrorockets would just be firing in a useless spiral as the stage tumbled. They would have to totally redesign the control software code too. Obviously they SHOULD but they clearly WON'T. Looks authentic. Only likely authentic video we have seen so far. Too bad it is so short and grainy. I did a review of all the fake rocket breakup videos circulating on social media: (link if it fails to properly embed again) There were a lot of them. So frustrating. I believe the Falcon upper stage has four ways to ensure a safe disposal: Final Merlin engine relight to target disposal trajectory Propulsive vent to target disposal trajectory Cold-gas ullage thruster impulse to target disposal trajectory Active cold-gas attitude control to control drag and re-entry profile And of course they also typically use a fairly low-altitude parking orbit to try and ensure the fastest possible deorbit. Obviously 3 and 4 are mutually exclusive; if you blow all your ullage gas then you can no longer control drag, so if your ullage reserves don't give you enough dV to get the disposal orbit that you want, you don't want to waste it. That's what happened back in March...the relight failed and (presumably) the propulsive vent wasn't quite enough to get a good disposal orbit, so they just went with active drag control to try and get re-entry as close to the water as possible. But there is a huge difference between having multiple safety measures and having those safety measures partially fail...and having no safety measures at all and flipping a coin on every launch, like the Long March 5B. You typically do have an FTS, but once you are in a stable orbit that FTS is irreversibly disarmed (usually a physical pin or arm that is dropped into place with a spring to prevent the FTS from firing and cannot be remotely removed). That's the callout you always hear during Falcon 9 webcasts right before SECO: "FTS is safed." You disarm your FTS once you're in orbit because the risk of a Kessler-initiating debris cloud on orbit from an armed FTS is much much higher than risks of ground impact. Also the biggest issue with the Long March 5B booster was those two stinking engines. Each YF-77 is the size of four-wheeler but weighs as much as a pickup truck. FTS is great for unzipping a stage and dumping propellants in midair to prevent a fireball on ground impact, but it does nothing to reduce the impact of a three-tonne chunk of flaming metal.

The propellant entry temperature for an NTR is not really particularly important, actually. The NTR doesn't particularly care what temperature the propellant is before it enters; it merely cares what temperature it can reach before melting. No, that's not true. A solid-core NTR has the same operating temperature whether it's running on liquid hydrogen, liquid methane, liquid nitrogen, or liquid milk. Seriously. You can put anything you want into an NTR and it will still have the same core operating temperature. Liquid hydrogen is best for NTRs not because it helps with cooling (although yes, you do need SOME regenerative cooling to keep your combustion chamber intact), but because it produces the maximum specific impulse at any given operating temperature. If you're running an old-fashioned NERVA at ~2100 K, liquid hydrogen gives you the highest specific impulse of any propellant. If you're running a ceramic metal composite like Dumbo at ~2500 K, liquid hydrogen gives you the highest specific impulse of any propellant. If you're using a rotating pebble-bed engine like Timberwind at just under 3000 K, liquid hydrogen gives you the highest specific impulse of any propellant. Any cryogen (or even water) will provide ample cooling for your engine; the engine operating temperature is limited by the engine design, not by the propellant choice. Liquid hydrogen is just the most efficient choice, primarily because of its low molecular weight. However, liquid hydrogen also sucks because it is so fluffy. If you're writing a sci-fi where they are using ISRU to refill the propellant tanks of an NTR-powered spacecraft, keep in mind that your vehicle's propellant capacity is going to be volume-limited, not mass-limited. Depending on the size of your tanks, you may end up with more delta-v if you fill up with methane or ammonia or even plain old water.

China. Task failed successfully.

It's all coming from international (non-Chinese) sources. China keeps insisting there is no danger and that it will definitely come down in the water. They have a 72% (by my latest numbers) chance of being right, so they're bluffing. For any of y'all here in the States, I did a ground track map. The chance of it re-entering over the United States is 5.85%. If it does come down over the United States, the breakup could be visible for up to half the country. The most likely re-entry path (that will be visible to the U.S. at least) will be the one that goes from Texas to Delaware between 12:49 AM and 12:55 AM EDT. Coincidentally that's also the one that's most likely to drop debris on me. If current predictions hold until morning (that is, if the window narrows about 50% without moving) then the odds of entry in Asia, Australia, South America, or the Mediterranean will be negligible and it will be the ocean at 74%, Africa at 11%, and North America at 9%.

I mean kind of yes. It's stated pretty clearly in the Constitution and we've had a couple centuries of jurisprudence saying so.

The actual amount of water coverage in this particular region is about 74% so it's a little less ideal.

The paths shift constantly as the stage decays so any path could change. Last update for the night.