sevenperforce

I will say, for the record, that while I would have absolutely no qualms about riding a reused booster or a reused capsule, I would be a touch nervous about riding with a reused, ablative heat shield. Even if it is supposed to be reusable multiple times. A reused non-ablative heat shield is fine, of course.

I made a video because of course I did. https://vm.tiktok.com/ZTdCSXEoy/ I will say that their Mars lander design is…within margins…decent? If you’re going to design a Mars lander with no purpose other than to get down to the surface and then back up to orbit, then it does make sense to use the approach they propose. Conical aeroshell with a big-cheeks heat shield, pop some supersonic chutes just to stabilize and allow you to drop the heat shield, and then use supersonic retropropulsion and land. Hypergolics and multiple engines for reliability. Drop the aeroshell, legs, and landing-prop drop tanks for single-stage ascent in an unpressurized capsule, just like Mark Watney.

By the time you get to burnout, thrust will have dropped below one gee, meaning that it will start to lose velocity due to gravity drag before it completely burns out. But if you calculate the specific impulse and then the delta-v, you can deal with a lot of this easily. I have absolutely no idea what your drag coefficient looks like. Honestly, I think you would do better with fewer, larger fins, but that’s completely heuristic advice so your mileage may vary. Without any concept of your velocity-specific drag coefficient I can’t hope to speculate about your rocket’s actual performance, but what I can do is put an upper limit on your apogee, based on what you’ve said. Specific impulse is the inverse of fuel-flow-specific thrust and can be calculated as the thrust divided by the propellant mass flow rate. Fortunately, you’ve provided both. Unfortunately, you don’t have constant thrust. I could assume that you’re using a pressure-fed propellant-blow-down design, resulting in a linear mass flow drop rate, but since I’m just going for the upper limit, I don’t need to. Your max thrust is 44 Newtons, which divided by 0.035 kg/s gives us a specific impulse of 1,257 m/s or 128 seconds. What’s your propellant combination and chamber pressure? Not that it matters for calculating the apogee; I’m just curious. You’re getting choked flow, right? Anyway, if you apply the Tsiolkovsky rocket equation, you get a total dV of 156 m/s. However, you’re dealing with gravity drag. Ten seconds of gravity drag robs you of 98.1 m/s, so your actual effective dV is going to be 58 m/s. So that’s your theoretical maximum burnout velocity. Given the thrust curve, mass gradient, and burnout velocity, plus the generous and inaccurate assumption of negligible aerodynamic drag, anyone equipped with first-semester physics can calculate an apogee.

It doesn’t look like you’re having trouble keeping thrust steady; it looks like you’re using propellant blow-down, and so the thrust drops off more or less linearly. Slope of the thrust curve appears to be around -2 Newtons per second. Obligatory: please be safe. Don’t be anywhere close to the thing when you light it. Obey all local laws and don’t assume you know what the laws are. Make sure there is absolutely 0% chance that anything flammable is downrange. That said, this is a fairly simple kinematics problem. If your engine burns an average of 35 g/s then your mass will be (at 1-second intervals, in kg): 3.0-2.965-2.93-2.895-2.86-2.825-2.79-2.755-2.72-2.685-2.65. Newton’s First Law helpfully reminds us that F=ma, so a=F/m. Liftoff acceleration will be 14.67 m/s^2 and burnout acceleration will be 8.3 m/s^2. However, gravity will be tugging the rocket back down toward terra firma the whole time at a cruel 9.81 m/s^2, so the actual liftoff acceleration will be 4.86 m/s^2. 10 km/hr is 2.78 m/s, so your rocket will exceed stabilization speed 0.57 seconds after launch. Assuming constant thrust for simplicity and starting from a standstill, x = a(t^2)/2, so your rocket will cover 0.79 meters before reaching stabilization speed. However, this doesn’t account for factors like the drag of the stabilization system or the drag with the launch rail interface or startup thrust gradients or any other number of variables. So to be safe you should probably do a 200% safety factor and make your launch rail about 2.4 meters high.

461 seconds is an absolute dream. Wow.

I didn't think Skyhooks were supposed to reach that low? Perhaps as low as 30 miles, well above the weather? Wiki says 100km or higher... https://en.wikipedia.org/wiki/Skyhook_(structure) Yes, correct. Skyhooks don’t come down to the surface by any means. And you spin the skyhook end-over-end in the same direction as the orbit, so the end that enters the atmosphere is moving quite slow compared to orbital velocity.

Is there confirmation of these larger Starlink sats?

Looking back at the “hot test” I can confirm that it was “hot” but I’m not sure it qualifies as a “hot fire” test except to the degree that it was hot and involved fire. I have yet to see any evidence that they have been able to produce sustained thrust. If you go look at their website, the shape of their thrust chamber and engine bell seems wildly wrong. I wonder if they’ve ever produced thrust higher than the sum of their pressurant systems.

I wouldn’t call it neo-divine either. The origination of new species under our guidance wasn’t necessarily even intentional; it was just an accident of history and circumstance, not unlike the beavers changing their local ecosystem. My point about cows, and everything else we’ve done, is more quantitative than qualitative. If you look at our energy consumption, our access to resources, and our knowledge of our planet, we are objectively quite close to being Kardashev-I. It would take something like ten Earths to provide the current human population with a Western-consumption-level lifestyle. And so without any qualitative or moral analysis at all, we end up with the realization that expansion (which we seem incapable of avoiding) is necessarily going to take us off-planet. Why do we find value in the concept of being remembered?

It’s for her pleasure. I’ll see myself out. In all seriousness, what are we looking at, exactly? Is this door going to slide open or fold open? And if it’s going to carry Starlinks, does that mean it will actually do a true orbital insertion rather than the quasi-orbital once-around? Or is the door just there to test deployment without actually deploying anything? And what is actually going to happen to B4/S20? Are they going to be just summarily scrapped? Will they use B4 for arm catching tests? Will they use S20 for P2P hop testing?

Everything about space flight has got to feel amazing but I have to imagine the sensation of docking is UP THERE.

There would have to be a history of bad acts, like price-fixing conspiracies, before the government would have a basis to break up SpaceX in any way. One bad act is predatory pricing. If a large market player with significant capital drops its prices very low in order to drive other competitors out of business, planning to increase those prices dramatically in order to recoup, then that can be actionable under the Clayton Act. However, that only happens if (a) the business is actually pricing below cost, and (b) the business has a substantial likelihood of being able to recoup. The launch services market is unique in this regard. Even though SpaceX can offer substantially lower-cost launch services than any competitor, without pricing below cost, the launch customer base still selects other companies. Even if SpaceX did lower its prices below cost, there’s no evidence that this would actually hurt other launch providers any more than they are already being hurt. Which is probably one reason why SpaceX doesn’t lower its launch prices any more than where they currently are. If Starship, etc. DOES drive every other launch provider out of business, and THEN SpaceX jacks Starship launch costs up…that’s still not actionable because SpaceX acquired this monopoly simply by being the best. A natural monopolist can charge a monopoly price (the monopoly price being the price which maximizes both the number of sales and profit per sale). Amusingly, though, the Starship monopoly price is probably fairly low because SpaceX will make more money in the long run by maximizing the number of launches than by maximizing the profit per launch.

I’m pretty sure Elon has enough skin in the game to nip THAT in the bud. No, refusal to deal can be a violation of the Clayton Act. If a company with a natural monopoly (like SpaceX) refuses to extend the same contracts to a potential competitor (like Amazon’s Kuiper) that it extends to otherwise-identical customers, that can be viewed as an unlawful expansion of monopolization in restraint of trade. I think SpaceX would be in the clear here, for numerous reasons, but it is still a potential refusal-to-deal claim. That’s what we were discussing. This is such a unique market that it’s hard to know how it should be structured or regulated. And the fact that the upstart is now the monopoly is a huge wrench as well. Monopolization by dint of natural prowess/ability is not precluded by the Clayton Act. You can absolutely monopolize a market by being the best as long as you don’t do anything fishy to get there.

I was discussing this in my antitrust law class on Tuesday. Would the DOJ and FTC accept a merger between BO and ULA on the theory that they could compete against SpaceX more effectively? What about a Rocketlab/SpaceX joint venture, using the Photon bus with Starlink tech? And if Amazon actually did seek launch services from SpaceX and SpaceX refused, would that be actionable as failure to deal?

I will note, for the sake of pedantry and associated motivations, that cows no longer be cows. The qualia that is Black Angus bovid existence did not exist before humans and would not be able to exist without humans. We may be small in comparison to the cosmos, but humans loom large over this planet. There was once a time where we competed with other species, but that time is long past. Now, the dominant reproductive fitness landscape of this planet is utility to humans. Hence the Black Angus. I am not so concerned with human extinction as I am with the extinction of knowledge and consciousness. I would argue that there is an essential moral imperative (to the extent that any morality is essential) to preserve knowledge. As a society, we recognize that it is fundamentally wrong to eradicate the lifestyles and cultures of indigenous peoples. We expend enormous energy seeking to understand and document the histories of long-extinct cultures. It is the light of consciousness and knowledge, not the accident of human biology, which we properly seek to preserve.

Word on the street seems to be that SpaceX is using these flights to expand (no pun intended) on their existing IVA suits in order to make them more versatile and suitable for EVA. We are still a far cry from surface sortie suits or independent maneuvering suits, but these suits will probably have some significant differences as compared to the prior IVA suits.

The nonsense “SLS to Mars” aspirations existed in an alternative universe where Block 1B was launching multiple times a year starting in 2018. And even that probably wouldn’t have quite the cadence needed for a flags-and-footprints Mars mission.

No, the reefing line is cut specifically by pyrotechnics or some other mechanism; it doesn’t open automatically.

The trouble with testing it is that there are various failure modes for a chute and really no way of testing all of them. Like, how can you simulate all possible ways that a filled chute can fail AND then impact other chutes, let alone test it? Even if you found simulations where the failure of a filled chute would impact the other chutes, it would be prohibitively difficult to induce that exact interaction in a test scenario to see what would actually happen. It should also be noted that they cannot conduct any test of this with a weighted frame as they have done in the past, because the chute-fill delay is the result of airflow interactions which depend not only on the other chutes but also on the shape (and presumably the COM) of the capsule. So you’d need a boilerplate capsule with sufficient fidelity to produce the same airflow interactions. What if they designated one chute as the “backup” and intentionally kept it reefed longer than the others? If I recall correctly, the fourth chute starts off inflated while reefed but then deflates when it is unreefed. A reefed chute needs less airflow to stay inflated than an unreefed one.

No, this is a bad take. It's subtle, but the 4th chute is not a "backup". The system has no backup -- if it fails, you have a fatal event. But there is some redundancy -- only 3 of the 4 chutes need to work. However, filled chutes can fail. The system is not successful until the capsule is all the way down at a safe speed. This is why I think that if they investigate this and discover that the 4th chute is still opening correctly, just slower, it's OK. But if they find that there is a serious risk of it not opening at all, this is a massive safety issue. Because at that point you no longer have redundancy, and your safety design was based on having redundancy. I think you misapprehend. I didn’t say that the fourth chute didn’t need to open; I said that it is fine if the system “opens a backup afterward.” As you point out, it WOULD be a problem if the fourth chute never opened, but that’s not what we have seen so far. There is a potential failure mode here. If three chutes open but the fourth chute has not opened yet, and then one of the three open chutes fails, what happens? Presumably this would accelerate the opening of the fourth chute (since it is no longer leeward of the chute that failed) and everything will be fine. It is possible that one of the three could fail in a way that causes it to become entangled with the fourth chute and prevent it from fully opening, but that’s really no different from a failed chute becoming entangled with one of the other filled chutes and causing it to fail in that fashion. So that’s a known failure mode anyway. All the public data so far indicate that delay in the fourth chute opening happens if and when the first three chutes open properly.

Why is that weird? It’s one of the many possible configurations in the Falcon family, each with gradually increasing payload capacity: F9, booster RTLS F9, booster boostback to ASDS F9, booster to ASDS (no boostback) FH, side boosters RTLS, core boostback to ASDS F9, booster expended FH, side boosters RTLS, core to ASDS (no boostback) FH, side boosters RTLS, core expended FH, side boosters boostback to ASDS, core expended FH, side boosters to ASDS (no boostback), core expended FH, all boosters expended The only thing I’m unsure about is exactly where an expended F9 (#5) fits in this progression. It may be more capable than tri-core-recovery FH without core boostback. But apart from that, each of these configurations has higher capacity than the last, and each of these configurations costs more than the last. So if the desired payload can’t be delivered with configuration #6 but can be delivered with configuration #7, then you pick #7 because there is no need to spend more money on #8. Well presumably FH doesn’t have the dV to do it while recovering the core. And presumably Psyche doesn’t need the extra dV that would be gained from ASDS recovery of the side boosters.

The fourth parachute is essentially a backup. It was designed to land optimally with three chutes. So a design which functions with three parachutes and then opens a backup afterward is fine…even if you don’t know which chute will act as the “backup” in advance.

Presumably this gives us new benchmarks and data about Falcon 9 capability.

Yeah you can’t do that. Velocity doesn’t scale proportionally to specific energy. You’ve got to sum the energies first, figure out what kind of chamber pressures you can handle, and go from there. If you don’t want to do all that math then you can approximate by saying that velocity scales with the square root of specific energy.

I don’t think the math on this works, even setting aside the issue of hot oxygen in your reactor. Preheating your propellants doesn’t raise your final combustion temperature significantly higher than it would already be, and since your specific impulse is dependent (to a first order) on combustion temperature, you’re not really gaining anything.