Quote from: envy887 on 02/24/2017 10:35 pmQuote from: Lars-J on 02/24/2017 09:10 pmYes, people don't seem to be grasping the size difference going from F9/FH to ITS. Putting a mini-ITS on a scale that most propose on FH would be like putting a F9 upper stage on a F1 first stage. It is just too big.A version that is 1/6 or 1/8 the mass would work fine on FH. It would be only slightly larger in diameter than the current fairing, but would have much better performance than the current stage.But when you scale something *that* small, it is no longer super helpful beyond verifying the most basic stuff. Scale changes things, it changes how air flows around the vehicle, and it changes how much heat needs to be dissipated, and so on.
Quote from: Lars-J on 02/24/2017 09:10 pmYes, people don't seem to be grasping the size difference going from F9/FH to ITS. Putting a mini-ITS on a scale that most propose on FH would be like putting a F9 upper stage on a F1 first stage. It is just too big.A version that is 1/6 or 1/8 the mass would work fine on FH. It would be only slightly larger in diameter than the current fairing, but would have much better performance than the current stage.
Yes, people don't seem to be grasping the size difference going from F9/FH to ITS. Putting a mini-ITS on a scale that most propose on FH would be like putting a F9 upper stage on a F1 first stage. It is just too big.
But when you scale something *that* small, it is no longer super helpful beyond verifying the most basic stuff. Scale changes things, it changes how air flows around the vehicle, and it changes how much heat needs to be dissipated, and so on.
Quote from: Lars-J on 02/24/2017 11:04 pmBut when you scale something *that* small, it is no longer super helpful beyond verifying the most basic stuff. Scale changes things, it changes how air flows around the vehicle, and it changes how much heat needs to be dissipated, and so on.That's why engineers use dimensional analysis. There is no reason to suggest that a half scale model is not useful. Wind tunnel tests at much greater differences of scale can be extremely accurate and revealing, especially if the models have dynamic similitude.
I think there may be no other option for him than to develop a mini ITS architecture. Currently all his revenue comes from being the most cost effective way of getting into LEO and other earth orbits. However Bezos is building what could evolve into a fully reusable system to get into similar orbits based on a raptor like engine. To stop Bezos eating his lunch I would think he needs to look at development of a raptor powered F9 replacement with a reusable upper stage. He could use the falcon heavy with reusable upper stage but hard to see how that would be competitive against Bezos single stick approach
Basic stuff like methalox storage and transfer on orbit? Raptor Vac coast and restart?But the main advantage would be putting similar payload to a better GTO orbit than Ariane 5, with a fully reusable system. And beating DIVH payload to direct GEO insertion if fully expended. Falcon Heavy doesn't have either of those capabilities now, and both could be worthwhile in the current market.
An alternative would be to have a full size (dimensions) ITS prototype, but at lower performance.So lower numbers of lower thrust Raptor on the booster. Only part fill the tanks. Aim for 50 tonnes of payload, rather than 300 tonnes.
Quote from: MikeAtkinson on 02/21/2017 08:53 amAn alternative would be to have a full size (dimensions) ITS prototype, but at lower performance.So lower numbers of lower thrust Raptor on the booster. Only part fill the tanks. Aim for 50 tonnes of payload, rather than 300 tonnes.Agreed.Earlier in this thread I had proposed simply flying a fully mfg tooled, partially fueled ITS with initially just 3 seal level Raptors sub-orbitally. Maybe move to an interim all SL Raptor test vehicle or maybe not.Followed by a fully mfg tooling sized booster stage but partially fueled with just 21 Raptors. Fly and recover, then next it's enough to launch a SL & vac ITS with close to zero payload into LEO to test re-entry.I ran some rocket equation #s and this seems to work. And so on...As someone who has developed hardware/software systems with 5 9s reliability goals my view (yes, I know I'm not aerospace experienced) is that sub scaled vehicles will only increase your already expensive tooling costs, delay final schedules and won't give the exact test results that flying your actual base hardware configuration does. Too many unknown unknowns in scale models.
..., the ITS will be tested as Musk outlined in his Powerpoint show. He can't afford the dollars and more importantly to him personally the TIME wasted in mini-ITS whatevers that do not lead directly to his goal. Per his presentation, instead of building & testing the 42 engine booster first, he moves right to the 2nd stage. Here's one scalable, incremental, direct pathway SX engineers could follow.Build the simpler to outfit 90 tonne ITS stage 2 Tanker version first.Equip with just the 3 SL Raptors to flight test them and the stage 2 airframe, TPS & avionics~700 tonnes of propellant and the 90 tonne craft can get up to ~5 Km/sec (rocket equation)Fly & recover, testing heat shield and airframe at lower stress and qualifying the avionicsNext build initial booster stage with ~ half the engines, but full sized airframe & tanks (no extra tooling costs)Maybe equip 2nd stage with some Rvacs, or do so later after 1st flightsThenExecute orbital tests & re-entry with minimal "payload" to LEOProves out landing technique for booster stage & more Raptor engine flight experienceand so on...I'm convinced SpaceX's engineers will come up with a more clever, lower cost approach than this, an approach that does not divert them from their goal and require non-essential R&D time and money for spacecraft not utilized in the Mars settlement core mission.
I think there may be no other option for him than to develop a mini ITS architecture. Currently all his revenue comes from being the most cost effective way of getting into LEO and other earth orbits. However Bezos is building what could evolve into a fully reusable system to get into similar orbits based on a raptor like engine. To stop Bezos eating his lunch I would think he needs to look at development of a raptor powered F9 replacement with a reusable upper stage. He could use the falcon heavy with reusable upper stage but hard to see how that would be competitive against Bezos single stick approachSomething similar in shape to ITS would make sense. It could have a cargo and manned version and would be capable of moon missions etc if it's used semi permanent ITS tankers in orbit. Cargo version would be first to meet commercial requirements. But down the track a crewed version would also have much greater crew capacity than the dragon2 if such a requirement was to evolve.
yesi had surgery today and i came out of the haze to say this.There have been a lot of threads about this. the conclusion always is that it is a waste of time and money, and actually slows things down. OP should do their homework and link to all of them. Why is this time different?
The area of a sphere goes goes up as the square of the radius, the volume rises by the cube.
Quote from: Lars-J on 02/24/2017 11:04 pmQuote from: envy887 on 02/24/2017 10:35 pmQuote from: Lars-J on 02/24/2017 09:10 pmYes, people don't seem to be grasping the size difference going from F9/FH to ITS. Putting a mini-ITS on a scale that most propose on FH would be like putting a F9 upper stage on a F1 first stage. It is just too big.A version that is 1/6 or 1/8 the mass would work fine on FH. It would be only slightly larger in diameter than the current fairing, but would have much better performance than the current stage.But when you scale something *that* small, it is no longer super helpful beyond verifying the most basic stuff. Scale changes things, it changes how air flows around the vehicle, and it changes how much heat needs to be dissipated, and so on.The area of a sphere goes goes up as the square of the radius, the volume rises by the cube. Sub-scale models may be of value in terms of technology development, but in areas where basic physics define your spacecraft (like hypersonic retro-propulsion) then the gain is an illusion. A smaller ITS - call it the ITS-SP after the 747-SP - is only of value if it fills a market niche, eg for LEO or Lunar/HEO missions, and it may well be that simply flying a standard ITS half-empty would also fill that niche, and without any unique development or manufacturing costs.
The "unique development or manufacturing costs" for ITS are the gigantic booster and 12m infrastructure. A 1/6 volume mini-ITS at ~375 tonnes GLOM for the upper stage + payload and ~6 meter diameter could fly on Falcon Heavy. That means all the existing infrastructure can be used: build in Hawthorne, truck overland, test in McGregor, process in the 39A HIF, launch on 39A with minimal modifications to the TEL and pad.
Quote from: envy887 on 03/02/2017 01:58 pmThe "unique development or manufacturing costs" for ITS are the gigantic booster and 12m infrastructure. A 1/6 volume mini-ITS at ~375 tonnes GLOM for the upper stage + payload and ~6 meter diameter could fly on Falcon Heavy. That means all the existing infrastructure can be used: build in Hawthorne, truck overland, test in McGregor, process in the 39A HIF, launch on 39A with minimal modifications to the TEL and pad.No, A 6 meter diameter payload is NOT easily truckable. SpaceX settled on a maximum practical diameter of 3.7m for F5/F9 because of highway transport limitations.Bigger things can be transported, but the roads you can use dwindle fast as the size goes up.
And the "niche" filled would be 15 tonnes to GTO fully reuseable. Plus demonstrating orbital refueling, high-energy lifting VTOL EDL, and the chance to land 50 tonnes on Mars or the Moon. Basically the entire ITS paradigm without most of the massive infrastructure investment.
Quote from: envy887 on 03/02/2017 01:58 pmAnd the "niche" filled would be 15 tonnes to GTO fully reuseable. Plus demonstrating orbital refueling, high-energy lifting VTOL EDL, and the chance to land 50 tonnes on Mars or the Moon. Basically the entire ITS paradigm without most of the massive infrastructure investment.I'm not a rocket scientist, so it's not clear to me why the vehicle could only put 15 tonnes in GTO but land 50 tonnes on Mars or the Moon. Could you explain that? Seriously, no snark intended.