Both Musk and many people here think it would be wasted effort. I think it could have the advantage of building something to use as a fully reusable workhorse launcher (replacing the F9), especially since SpaceX is developing a scaled down Raptor engine contracted by USAF anyway.
Quote from: philw1776 on 02/17/2017 06:27 pmBuild 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 avionicsI like that approach, a lot. As far as I remember, a completely new suggestion that makes a lot of sense to me. But I am not an expert.
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 avionics
Quote from: uhuznaa on 02/17/2017 12:27 pmBoth Musk and many people here think it would be wasted effort. I think it could have the advantage of building something to use as a fully reusable workhorse launcher (replacing the F9), especially since SpaceX is developing a scaled down Raptor engine contracted by USAF anyway. Yea, this was discussed on a similar thread. Myself, I don't think there's a case for a mini-ITS. For the same reason there was no real need for a "Saturn III" between the Saturn 1B and Saturn V. For going to LEO, the Saturn 1B was fine. For sending humans BLEO, you need as much capability as you can get, so you wanted the Saturn V (or even bigger, if it has been feasible). But not much need in between. Not even as an interim stepping stone. NASA went right from the Saturn 1 to Saturn V. It's similar for SpaceX. They already have their "Saturn 1" in Falcon, and now they want as much capability as they can possible get in ITS. No need to have an intermediate LV. It is nice to work up in scale, but it also costs a lot to have an entirely new and different intermediate LV to pay for development and testing. Go do what you really -need- and then focus your funds and efforts there. Rather than an essentially "dead end" LV.NOTE: The one scenario it could make sense, is as a fully reusable Falcon replacement. Something that would handle all commercial and government payloads fully reusably in a single stick LV. Something that could launch basically a D4H payload to GTO, have the booster RTLS, and have the upper stage deploy the payload in GTO, and then have enough propellants to deorbit itself form GTO, and land back at the launch site. The problem with this, is they already have Falcon in place and all of it's development paid for. It's probably not the LV they'd be flying if they could do a clean sheet design knowing everything they know right now, but as the bumper sticker says, "Don't laugh, it's paid for". ;-)They have launch pads being built for Falcon, and infrastructure in place for it. And a mini-ITS to replace it would have to be built somewhere near the water or at the launch site like ITS since it couldn't be transported by road...which means starting all over again after they've just barely got their final version of Falcon flying, and FH soon to be flying. So I don't see them scrapping all of that and starting over, just to replicate the capabilities F9/FH will already have...just with an expendable upper stage rather than a reusable one.
Good points, but I see a problem with your comparison.Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.
Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.
Quote from: Lobo on 02/21/2017 06:53 pmQuote from: uhuznaa on 02/17/2017 12:27 pmBoth Musk and many people here think it would be wasted effort. I think it could have the advantage of building something to use as a fully reusable workhorse launcher (replacing the F9), especially since SpaceX is developing a scaled down Raptor engine contracted by USAF anyway. Yea, this was discussed on a similar thread. Myself, I don't think there's a case for a mini-ITS. For the same reason there was no real need for a "Saturn III" between the Saturn 1B and Saturn V. For going to LEO, the Saturn 1B was fine. For sending humans BLEO, you need as much capability as you can get, so you wanted the Saturn V (or even bigger, if it has been feasible). But not much need in between. Not even as an interim stepping stone. NASA went right from the Saturn 1 to Saturn V. It's similar for SpaceX. They already have their "Saturn 1" in Falcon, and now they want as much capability as they can possible get in ITS. No need to have an intermediate LV. It is nice to work up in scale, but it also costs a lot to have an entirely new and different intermediate LV to pay for development and testing. Go do what you really -need- and then focus your funds and efforts there. Rather than an essentially "dead end" LV.NOTE: The one scenario it could make sense, is as a fully reusable Falcon replacement. Something that would handle all commercial and government payloads fully reusably in a single stick LV. Something that could launch basically a D4H payload to GTO, have the booster RTLS, and have the upper stage deploy the payload in GTO, and then have enough propellants to deorbit itself form GTO, and land back at the launch site. The problem with this, is they already have Falcon in place and all of it's development paid for. It's probably not the LV they'd be flying if they could do a clean sheet design knowing everything they know right now, but as the bumper sticker says, "Don't laugh, it's paid for". ;-)They have launch pads being built for Falcon, and infrastructure in place for it. And a mini-ITS to replace it would have to be built somewhere near the water or at the launch site like ITS since it couldn't be transported by road...which means starting all over again after they've just barely got their final version of Falcon flying, and FH soon to be flying. So I don't see them scrapping all of that and starting over, just to replicate the capabilities F9/FH will already have...just with an expendable upper stage rather than a reusable one.Good points, but I see a problem with your comparison.Saturn 1B and Saturn V are similar rockets as in they used similar construction and fuel. ITS will have composite fuel tanks and use methane instead of RP-1, major changes from F9. That's a bigger leap than going from Saturn 1B to Saturn V. But it looks like Elon is comfortable with making that leap.
Keep in mind that scale models are usually (?) done as proof of concepts. Some of the more successful scale models (DC-X) focus more on specific technologies. Scale models that try to do to much - replicate everything at a smaller scale - like X-33 can run into problems.So the question is... what specific kinds of challenge technologies do you hope to test and verify using a "small ITS"? And is verifying those really that much more cost-effective using a smaller scale?I'll start by pointing out three things I see as big challenges:- ITS reentry shape (scale changes mass properties, for example going from Apollo to Orion was more difficult and costly than imagined *despite* same shape)- ITS TPS (similar concern as above, scale affects mass and heat loading)- structural composite cryogenic tanks (this testing can be done all on the ground, no smaller vehicle needed)
I think arguing for a smaller final ITS system because it would be more affordable is one argument that I might agree with. But I don't think creating a smaller pathfinder system is worth it.
It's scale is huge, sure.But we need to remember that ITS would be a paradigm shift. And we have to stand on our heads a bit to account for that. It's huge...but fully reusable...with not only booster recovery and reuse, but "return to launch site" recovery and reuse. Right now F9-FT is technically much larger than necessary for what it needs to do. But it's grown larger and more powerful as SpaceX has explored booster reusability. It uses that extra performance to land the booster on a barge or back on land, depending on payload requirements. But they've squeezed about as much performance out of the hardare and technology as they can. If SpaceX could redesign Falcon 9 from scratch today, knowing everything they know now, and if road transportation wasn't a consideration, I think it'd be even larger...and probably methane, which would make it even larger yet as CH4 is less dense than RP-1. That way they could launch all the commercial sats to GTO and still RTLS the booster...which is ideal. They may even go larger yet, and get up into EELV-heavy payload range and RTLS the booster, but without the need for the complex tri-core booster. That way they have just one common single-stick booster for pretty much every potential payload, and it could return the booster to the launch site for all of them. Now, if you added a reusable upper stage to that, then your scale goes up again to account for that. But while very oversized, it could still be very economical.ITS is just really an extension of that.
Yes, I've discussed that before with some folks, I think on the Mini-BFR thread.The ITS Spacecraft is really it's own SSTO rocket. It will have to get itself off the surface of Mars and get itself all the way back to Earth and land. It needs help on Earth to get itself all the way over to Mars because of the deeper gravity well, with a usable payload, but without much (or any) payload, it could probably get itself up to LEO on it's own...with some engine modifications as it can't take off with those vacuum nozzles.And with some tweaking later, it could probably get itself plus some usable payload to LEO. In which case, it could possibly replace Falcon at some point down the road. And given how it will be designed to operate on the surface of Mars, it could possibly operate on some large flat pad, or with a simple launch mount, like Redstone or the Early Saturn 1's. Although they will probably want to direct the thrust in some manner rather than have it go in all directions... and need some sound supression and other things that won't be an issue on Mars. But you get the idea. It could really change the whole idea of pad ops to something a little more like an airport. If not going to Mars, these spacecraft would launch and land themselves in one big flat complex to handle the typical comsat payload or crew shuttle duties to a space station. And it'd be just a different configuration of the hardware already built for the Mars program.
Quote from: redliox on 02/21/2017 02:31 amElaborate on scale models. I'm curious is there's an optimal scale that is best for testing, not to mention whether it's better to scale by volume or by mass.More recently, a deliberately scaled model of the Raptor engine was produced for testing, and has so far been successful. However, the test carbon fuel tank was almost full size for the ITS spaceship, and failed in an early test. With the benefit of hindsight, perhaps a smaller scale model would have been a cheaper first iteration?
Elaborate on scale models. I'm curious is there's an optimal scale that is best for testing, not to mention whether it's better to scale by volume or by mass.
Not suggesting there is anything wrong with your ΔV calculations, but when you talk about a scale model, that refers to a linear dimension, not to mass. What you are describing is roughly a 0.8 scale model of the ITS.
Quote from: OneSpeed on 02/18/2017 10:59 amNot suggesting there is anything wrong with your ΔV calculations, but when you talk about a scale model, that refers to a linear dimension, not to mass. What you are describing is roughly a 0.8 scale model of the ITS.How is that number, 0.8 generated? I assume it's not merely implying this instance of a mini-ITS is 80% the linear dimensions of a full-ITS. Same as a 4:5 ratio? How would that translate to both dimensions and mass?
Basically the ITS (especially if you're referring to its booster half) is the supreme evolution of Falcon tech eh?
If you're referring to the spaceship half of the ITS, mini or full, I disagree on re-purposing it for use on Earth. You may as well be asking the Apollo LEM to do likewise. The furthest the full-scale could go alone would be to LEO, but not to GTO or Luna so its applications would be limited much as the weight of the space shuttle's wings limited its operations. At Mars it could indeed a SSTO godsend, but it is going to be some time before Martian manufacturing gets setup.However, if you're talking about the ITS BOOSTER, you have a far better alley to tread. It's a beautiful example of what a HLV should be. The SLS, as an example, has more potential than the STS because it has cargo capacity unseen since Saturn's days; it's main limitations are it's Orion's mule and it is very old-school (since, during the Augustine days, it was viewed that the limited reusability of the shuttle was part of its downfall [since then SpaceX has improved on it heavily]). The ITS booster is a single rocket doing a superior job compared to either Falcon Heavy or SLS, both of which require setups of multiple rockets. I wouldn't wish to scale down the ITS booster even for simplicity-sake because it (and perhaps whatever Blue Origin can generate) would be the best rocket ever developed in either the 20th or 21st centuries!So, while this thread is meant to apply towards both the booster and spaceships halves of ITS, IMPO thus far I think any scaling should be done to the spaceship but not the booster. The booster is going to be used exclusively at Earth so obviously testing it here is easier whereas the conditions the spaceship encounters are literally on another planet. Outside of rocket fuel explosions, what precautions should be taken would be with the conditions the spaceship and its crew face on Mars, especially EDL.
Quote from: redliox on 02/21/2017 10:55 pmQuote from: OneSpeed on 02/18/2017 10:59 amNot suggesting there is anything wrong with your ΔV calculations, but when you talk about a scale model, that refers to a linear dimension, not to mass. What you are describing is roughly a 0.8 scale model of the ITS.How is that number, 0.8 generated? I assume it's not merely implying this instance of a mini-ITS is 80% the linear dimensions of a full-ITS. Same as a 4:5 ratio? How would that translate to both dimensions and mass?The 0.8 figure presumably comes from how mass scales with linear dimension change.For example... If you want an ITS that is half the liftoff weight of a full ITS, then the linear scale change is 0.8. (0.8 ^ 3 = ~0.5) So it is not going to be as much smaller as you might think.
The mini-ITS in this case would be 80% the same dimensions as its big brother...
That actually seems like a good thing. The mini-ITS in this case would be 80% the same dimensions as its big brother and light enough not to require a tanker to get to Mars. Handling how the mass would double would become the final issue; given how the test tank blew maybe a slightly smaller tank might be a wise start.
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: redliox on 02/22/2017 12:08 amThat actually seems like a good thing. The mini-ITS in this case would be 80% the same dimensions as its big brother and light enough not to require a tanker to get to Mars. Handling how the mass would double would become the final issue; given how the test tank blew maybe a slightly smaller tank might be a wise start.Why would the ship not require a tanker to get to Mars?