Of course. It does not make sense, from a physics perspective, to do anything other than a ballistic trajectory. Anything else will take a lot more energy and will cost much more, without significant benefit.
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Starship “EP2P” (Earth Point-to-Point) Discussion
- Thread starter ecarfan
- Start date
Of course. It does not make sense, from a physics perspective, to do anything other than a ballistic trajectory. Anything else will take a lot more energy and will cost much more, without significant benefit.
Thanks. If they can keep fueling cost down and can actually carry that many people, then they just need to work on other cost factors to make sure they can make money with these operations. BTW, for typical airlines, the fuel cost is usually 20% to 35% of their total operating cost. Hopefully EP2P can bring that % up so it can be more profitable.
I would assume there are still significant thermal issue to manage, unless they are going to find a way to re-enter atmosphere at supersonic rather than hypersonic speed.
Yah.
Actual fuel load will be much less than what I put due to non-orbital altitude and speeds, and I din't include the dry mass of BFR.
A350-900ULR carries 44,000 gallons, if you call it a 20% reserve, that is ~$80k in fuel costs.
The fuel budget may allow a lot of engine braking first if thermal is an issue. However, I don't think it will be due to speed being less than a normal re-entry. They have been working on non-ablative heat shield technology which will assist greatly.
X-15 skin temperature reach 1000F+ flying at Mach 6 in the atmosphere, and I would assume BFR during re-entering will be near that speed and temperature. Even if it can bring the speed down to high supersonic, it'll still need robust TPS since common composite material systems are not meant to operate in 200F+ environment. For example, Concorde reached 260F near its stagnation point at Mach 2.2 cruise, and most composite systems cannot handle that without significant degradation to its properties.
Also, non-ablative TPS is available and is used for number of high speed applications. They are quite expensive and typically very maintenance intensive.
BTW, I hope no one take my information/reply as a knock on the BFR EP2P. I think this is potentially the big breakthrough in commercial transport that many have been waiting for. But I also want to bring in some reality check since I work closely in this industry and know the challenges involved.
Falcon 9 Block 5 may have switched from cork to Pyron (may now be called Zoltek OX?) or similar materials for thermal protection. This Teslarati article mentions it is good to 1200 C. Similar materials are used for aircraft brakes
Totally made up numbers for fun:
From the Zolltek OX datasheet:
0.0330 W/(m*°K)
0.229 (Btu*in)/(hr*sqft*°F)
So a 10 mm layer will pass 3.3W per degree K (ignoring epoxy); with a 600 C delta, that is ~2kW/m^2 or twice the energy due to solar gain of a matte black surface.
The problem with a single pilot is that they might become incapacitated, or die, or need to go to the toilet. Zero pilots don't have any of these problems.
But who is there to fix the problem when a fault developed in the autonomous system? Today's commercial airplanes can basically fly themselves, but pilots are still needed. There has been pushed to reduce or remove pilots, but I really don't see that happening anytime in the near future unless the backup systems can be demonstrated to be near fail-safe.
Having crew on board to handle emergencies/ environmental controls/ anomalies is a good idea. However, the idea of being able to manual pilot a vertical reentry vehicle post computer failure seems really hard. Even if the engine control computer still worked after failure of the autonomous flight computer, would reaction time allow recovery of the flight profile?
Agreed, it'll be difficult. I would think it's similar to stall recovery for commercial airplane, some are easier and some are harder. But at the end of the day, it'll need to have multiple backups, whether human or computer, to significantly reduce probably of losing a vehicle due to system failures.
Oh for sure, triple computers at a minimum. If they swap vacuum for sea level engines, they might be able to fit two (3?) sets of triple redundant computers each with a set of engines sufficient to land the craft. If the engines can throttle to match gravity and there is sufficient extra fuel, a person (with computer stability assist) could possibly land it. If the system fail safes to a 5,000 ft AGL / zero velocity holding point on systems failure, the reaction time issue could be mitigated.
JRP3
Hyperactive Member
This video paints a fairly bleak picture for the idea of using StarShip for point to point travel on earth.
dhanson865
Well-Known Member
He tried to say it would be massively carbon positive (adding carbon to the atmosphere) when Elon has said by the point they offer this service it will be carbon neutral (using solar power to pull the fuel out of the air).
He also made a table compared to existing flights when this will open up new routes that aren't currently run.
In short I think that video on the whole is click bait more on the edge of incorrect than it is an accurate portrayal of his actual expectations or mine. He dials it back in at points so it's clear he is being sensational with the most negative parts of the video.
dhanson865
Well-Known Member
TIL starship only needs to carry more than 49 passengers to beat the longest commercial flight. Starship point to point travel might not be cheap but it covers a clear hole in commercial air travel capability.
Stepping past the decades+ of hurdles P2P human rocket travel has in front of it (decades in which the conventional air travel product will advance):
- Ultra long distances aren't at all a clear hole in commercial air travel. The capacity is basically there today and basically has been for some time now (20+ years); there really aren't any real markets that could be addressable only if equipment was available. Simply choosing a too-far-away city pair (as the linked YouTube does) doesn't properly address the fact that an ultra haul direct flight needs enough people that want to pay a premium to save 15-20% of their trip time to fill up a recurring schedule's worth of aircraft. The only way there's stable demand in that situation is if both cities in the pair are affluent enough--South America simply doesn't have that demand and widespread-enough affluence. If there really were a market for Beijing-Sao Paulo (for instance) you'd have China Airlines or LATAM doing 5th freedom flights and chomping at the bit for 22-24h equipment.
- That 49pax Quantas ultra haul flight (and maybe there were a couple more?) was research, not actually commercial service. Probably more of a stunt than anything because the flight time was only a bit longer than the ~19h NYC-Singapore routes (the current "longest commercial flights"), but in any case its another piece of evidence that there's not really a hole in commercial air travel. Despite the seemingly no-brainer element of connecting Sydney direct to backwaters like London and NYC, Quantas is approaching the concept very deliberately. We're still years out from those Sydney ultra hauls being a recurring/stable routes. And again, to friggin NYC and London.
- Max range of existing ultra haul equipment is no accident. It's not that it's technologically difficult, it's that there's just no demand to go farther. The market speaks.
- Humorously, NFW does any American rocket ever get close to China, so it's a pretty odd piece of evidence in favor of P2P rockets.
As regards arguing with me over the cost of shutting down a factory. You said you didn't know of a situation where hours = millions and I was attempting to give one, not that it justifies Starship cargo point to point, but because such things do exist.
Again, it was an example of hours = millions.
If it's 12 hours from supplier to factory and they are shut down, it can be worth millions.
That's all I was trying to say in my original 2 or 3 line reply.
Tagging @scaesare to unclutter main thread.
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Knightshade
Well-Known Member
I said I didn't know of a situation where hours=millions and that starship would solve
Which was the actual topic under discussion.
The article you then linked to didn't show that at all-- because it was citing days to resolve these issues due to the competent labor or parts needing DAYS to arrive on-site. That isn't a "speed of transport" problem that is an "availability of the fix to be transported at all" problem. Starship won't fix that.
Yes, I get the bulk of the article wasn't relevant. I only included it for the factory shutdown cost number.
If both the supplier and factory were near enough to Starship sites, it could be worth millions. Current alternative is hiring multiple private jets (which cuts buffering time).
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