Quote from: Citizen Wolf on 03/21/2016 09:07 am@93143I totally missed that the graph was referring to Sabre 4. Thanks for pointing that out. I know we all pretty much guessed that they were going to go with Sabre 4, AFAIK no official announcement has been made yet, but I guess going from that graph the decision has been made for Sabre 4.It is interesting that in that talk he made no mention of the fact that the frost control system was probably not going to be needed and mentioned that one person nearly let out the secret of it without pointing out that the patents are public and the secret is revealed anyhow. So why have the talks have continued following the "SABRE3" story? One reason could be that it allows them to give an interesting talk, impress everyone etc without giving away too much about their current train of thought.With regard to publicising talks, I can well imagine that they are not interested in publicity *that much* and are doing them for the money. If so it's a bit sad. I think amazing people are future shareholders :-)
@93143I totally missed that the graph was referring to Sabre 4. Thanks for pointing that out. I know we all pretty much guessed that they were going to go with Sabre 4, AFAIK no official announcement has been made yet, but I guess going from that graph the decision has been made for Sabre 4.
Quote from: RanulfC on 03/16/2016 09:12 pm*REL itself, while rightly pointing out that the Skylon is DESIGNED for SSTO operations and is more "efficient" at that design point given it's design assumptions, explains that the Skylon AS DESIGNED is capable of and could be used as the suborbital first stage of a two-stage mission. It's right there in the Skylon Users Manual cited earlier. Page 8-9 give orbital figures while page 10 is for suborbital deployment. Note in either case for anything other than LEO all payloads have to include propulsion to deliver to their required destination. As noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion. That's the C2 manual, it isn't in the D1 manual, and was (if I recall correctly) disavowed by the REL team
*REL itself, while rightly pointing out that the Skylon is DESIGNED for SSTO operations and is more "efficient" at that design point given it's design assumptions, explains that the Skylon AS DESIGNED is capable of and could be used as the suborbital first stage of a two-stage mission. It's right there in the Skylon Users Manual cited earlier. Page 8-9 give orbital figures while page 10 is for suborbital deployment. Note in either case for anything other than LEO all payloads have to include propulsion to deliver to their required destination. As noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion.
- but I personally suspect it's more because such activity is more the nailbiting style operations of vertical launch vehicle instead of the dull airline style operation they aim to achieve than for any show stopping reason.
Take out the SOMA, fuel cells and heavily insulated orbital tankage, lengthen (and strengthen?) the cargo bay and add some batteries you've got a reusable first stage to a TSTO launch vehicle. Perhaps slap a conventional jet engine in the SOMA hole and some inlet ducting to allow RTB.
As far as going single engine, it doesn't seem beyond consideration to divide the Sabre engine into an intake / turbopump assembly mounted centerbody, and rocket combustion chambers with nozzles in wing pods. But that would require high pressure plumbing between the separated pieces.
Quote from: Vultur on 03/17/2016 05:36 pmTrue. I think SSTOs would have a much stronger case if we had space tugs.However, with electric propulsion now being available to raise satellite orbits...The biggest change in REL's development plans was the introduction of the Skylon Upper Stage, which is a reusable space tug
True. I think SSTOs would have a much stronger case if we had space tugs.However, with electric propulsion now being available to raise satellite orbits...
The required delta-v from LEO (800km with the C2 or 600km for the D1) was always implied to be part of the "payload" mass to LEO carried by the Skylon. I think that was always one of the biggest confusions.Randy
Quote from: Paul451 on 03/19/2016 11:43 amQuote from: Radical_Ignorant on 03/19/2016 08:20 amSecondly, there is what Zurbin is arguing against: let's do multiple middle steps. Let's push the final goal so far away that till this time will come, everything will change.How's that worked out for Zubrin so far? He's now notorious for handwaving any problems in his own proposals while attacking any alternatives, to the point that I doubt anyone except a few rusted-on amazing people¹ take him at all seriously any more.The most he's achieved is to reduce support for other technology development programs.¹ Of course, one of those amazing people now owns his own rocket company. But ironically he practices the iterative development method I prefer.That's not fair. What progress NASA achieved in their goals to go to moon and Mars and... Other tech programs, like VASIMIR, which is, as far as I read abut it, over promised even in theory. Additionally that was the goal of Zurbin to "don't waste resources on unknown purpose technology". Addionally that he is little aggressive and unfriendly in manner of his speeches have nothing to do with validity of his arguments.
Quote from: Radical_Ignorant on 03/19/2016 08:20 amSecondly, there is what Zurbin is arguing against: let's do multiple middle steps. Let's push the final goal so far away that till this time will come, everything will change.How's that worked out for Zubrin so far? He's now notorious for handwaving any problems in his own proposals while attacking any alternatives, to the point that I doubt anyone except a few rusted-on amazing people¹ take him at all seriously any more.The most he's achieved is to reduce support for other technology development programs.¹ Of course, one of those amazing people now owns his own rocket company. But ironically he practices the iterative development method I prefer.
Secondly, there is what Zurbin is arguing against: let's do multiple middle steps. Let's push the final goal so far away that till this time will come, everything will change.
Quote from: john smith 19 on 03/16/2016 07:11 pmTo preserve the CoG protecting features you'd need to put it on top of the payload bay, like a sort of V1 cruise missile. But that would leave the issue of how you open the bay to get the payload out.Belly doors, obviously. (Loading would be via an elevator-pit.)
To preserve the CoG protecting features you'd need to put it on top of the payload bay, like a sort of V1 cruise missile. But that would leave the issue of how you open the bay to get the payload out.
Quote from: RanulfC on 03/16/2016 09:12 pmbut dropping off the excess mass of the booster stage and continuing the mission profile with a more efficient second stage that is fully reusable is as valid an assumption as not.If you're using SABRE, then you've got that backwards. You'd have a reusable first stage (the Skylon-derivative), with an expendable all-rocket, vacuum-optimized upper-stage.
but dropping off the excess mass of the booster stage and continuing the mission profile with a more efficient second stage that is fully reusable is as valid an assumption as not.
Original reply was lost in space/time Quote from: JCRM on 03/17/2016 12:42 amQuote from: RanulfC on 03/16/2016 09:12 pm*REL itself, while rightly pointing out that the Skylon is DESIGNED for SSTO operations and is more "efficient" at that design point given it's design assumptions, explains that the Skylon AS DESIGNED is capable of and could be used as the suborbital first stage of a two-stage mission. It's right there in the Skylon Users Manual cited earlier. Page 8-9 give orbital figures while page 10 is for suborbital deployment. Note in either case for anything other than LEO all payloads have to include propulsion to deliver to their required destination. As noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion. That's the C2 manual, it isn't in the D1 manual, and was (if I recall correctly) disavowed by the REL teamIt is in fact but still informative. If REL "disavowed" it they may want to take it off their website
Quote from: Hanelyp on 03/22/2016 02:00 pmAs far as going single engine, it doesn't seem beyond consideration to divide the Sabre engine into an intake / turbopump assembly mounted centerbody, and rocket combustion chambers with nozzles in wing pods. But that would require high pressure plumbing between the separated pieces.Is running that plumbing a show-stopper?
As I think about the single SABRE integrated into a fuselage I can see a couple of benefits compared to Skylon in addition to the challenges. With Skylon the wings need to be strong enough to support the SABREs on the ground, and any loads the SABREs would apply when flying/gliding during turbulence. More strength often means more mass. Their shape is presumably driven and even compromised by this - shorter wingspan is better for loads.
Quote from: Hanelyp on 03/22/2016 02:00 pmAs far as going single engine, it doesn't seem beyond consideration to divide the Sabre engine into an intake / turbopump assembly mounted centerbody, and rocket combustion chambers with nozzles in wing pods. But that would require high pressure plumbing between the separated pieces.Is running that plumbing a show-stopper? As I think about the single SABRE integrated into a fuselage I can see a couple of benefits compared to Skylon in addition to the challenges. With Skylon the wings need to be strong enough to support the SABREs on the ground, and any loads the SABREs would apply when flying/gliding during turbulence. More strength often means more mass. Their shape is presumably driven and even compromised by this - shorter wingspan is better for loads.The wings on an integrated SABRE/fuselage design can be shaped and sized for the aerodynamics alone.You also have a much simpler, more conventional shape for re-entry. (Although we've heard from REL that Skylon's unusual shape can re-enter just fine.) I'm confidently guessing drag would be lower too.So picture something like super-sized X-37B SSTO that takes off and lands on a runway. Throw in the V-tail from the X-37 and FASTT design for good measure so you don't need the transpiration cooled canards.Payload would be small compared to the twin SABRE Skylon, but perhaps a runway launched, responsive, reusable spaceplane would interest the USAF? Sort of like a next gen X-37.But all of this does hinge on the practicality of running that plumbing.
Quote from: RanulfC on 03/22/2016 02:47 pmOriginal reply was lost in space/time Quote from: JCRM on 03/17/2016 12:42 amQuote from: RanulfC on 03/16/2016 09:12 pmAs noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion. That's the C2 manual, it isn't in the D1 manual, and was (if I recall correctly) disavowed by the REL teamIt is in fact but still informative. If REL "disavowed" it they may want to take it off their website Having both versions shows how the design has been revised, so while removing it would be for claity I sincerely hope they don't.
Original reply was lost in space/time Quote from: JCRM on 03/17/2016 12:42 amQuote from: RanulfC on 03/16/2016 09:12 pmAs noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion. That's the C2 manual, it isn't in the D1 manual, and was (if I recall correctly) disavowed by the REL teamIt is in fact but still informative. If REL "disavowed" it they may want to take it off their website
Quote from: RanulfC on 03/16/2016 09:12 pmAs noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion. That's the C2 manual, it isn't in the D1 manual, and was (if I recall correctly) disavowed by the REL team
As noted above that's somewhere around 15mt to 18mt for Skylon delivery to orbit but the guide points out that Skylon can deliver up to it's maximum STRUCTURAL load of 30mt in a suborbital, two stage launch with payload supplied propulsion.
QuoteActually there was something of a "show-stopper" in the operation description; The Skylon had to be TOWED home after the suborbital mission which would indicate it used all its propellant getting the 30mt to suborbital velocity.I'm not sure why that's a show stopper? I've not seen an operational mode for Skylon that relights the SABREs (other than transitioning from air to LOX). Towing is their preferred method of site-to-site transport for Skylon
Actually there was something of a "show-stopper" in the operation description; The Skylon had to be TOWED home after the suborbital mission which would indicate it used all its propellant getting the 30mt to suborbital velocity.
QuoteTake out the SOMA, fuel cells and heavily insulated orbital tankage, lengthen (and strengthen?) the cargo bay and add some batteries you've got a reusable first stage to a TSTO launch vehicle. Perhaps slap a conventional jet engine in the SOMA hole and some inlet ducting to allow RTB.No the Skylon as designed isn't going to work for a first stage per-se. As noted even if you pull out the cited systems you still need to radically restructure the air/spaceframe to handle the new loads which is going to no longer make it a "Skylon" anyway.
Quote from: The Amazing Catstronaut on 03/22/2016 03:44 pmQuote from: RanulfC on 03/22/2016 03:39 pmThe required delta-v from LEO (800km with the C2 or 600km for the D1) was always implied to be part of the "payload" mass to LEO carried by the Skylon. I think that was always one of the biggest confusions.Which in-turn leads to a smaller true payload. Shuttle also had the capability to have an extra upper stage as payload capability, if I'm reading this thread right. As I understand it the Shuttle generally used the IUS, and the Centaur-G was designed to be flown (in Challenger or Discovery) but wasn't
Quote from: RanulfC on 03/22/2016 03:39 pmThe required delta-v from LEO (800km with the C2 or 600km for the D1) was always implied to be part of the "payload" mass to LEO carried by the Skylon. I think that was always one of the biggest confusions.Which in-turn leads to a smaller true payload. Shuttle also had the capability to have an extra upper stage as payload capability, if I'm reading this thread right.
The required delta-v from LEO (800km with the C2 or 600km for the D1) was always implied to be part of the "payload" mass to LEO carried by the Skylon. I think that was always one of the biggest confusions.
According to Mark Hempsell it's out.http://forum.nasaspaceflight.com/index.php?topic=34964.msg1272415#msg1272415
Quote from: adrianwyard on 03/22/2016 03:37 pmQuote from: Hanelyp on 03/22/2016 02:00 pmAs far as going single engine, it doesn't seem beyond consideration to divide the Sabre engine into an intake / turbopump assembly mounted centerbody, and rocket combustion chambers with nozzles in wing pods. But that would require high pressure plumbing between the separated pieces.Is running that plumbing a show-stopper? As I think about the single SABRE integrated into a fuselage I can see a couple of benefits compared to Skylon in addition to the challenges. With Skylon the wings need to be strong enough to support the SABREs on the ground, and any loads the SABREs would apply when flying/gliding during turbulence. More strength often means more mass. Their shape is presumably driven and even compromised by this - shorter wingspan is better for loads.The wings on an integrated SABRE/fuselage design can be shaped and sized for the aerodynamics alone.You also have a much simpler, more conventional shape for re-entry. (Although we've heard from REL that Skylon's unusual shape can re-enter just fine.) I'm confidently guessing drag would be lower too.So picture something like super-sized X-37B SSTO that takes off and lands on a runway. Throw in the V-tail from the X-37 and FASTT design for good measure so you don't need the transpiration cooled canards.Payload would be small compared to the twin SABRE Skylon, but perhaps a runway launched, responsive, reusable spaceplane would interest the USAF? Sort of like a next gen X-37.But all of this does hinge on the practicality of running that plumbing.I've considered similar notions, but always assumed REL must have considered and discarded the single in-line SABRE configuration. But now that the subject has been broached :-) ....In my thoughts, I assumed there would be a single (set of) combustion chamber (s) at the tail, further reducing the drag/wing-structure issues. I note that the exact placement of the intake + precooler could be tuned in order to maintain optimal CoG.Some other issues/advantages leap to mind:-Where would the bypass burners vent? It doesn’t seem impossible to have bypass air ducted all the way to the back of the vehicle. Many smaller ducts seem preferable, in order to maintain as straight a path as possible.-Heat transfer to the cryo tanks from that plumbing-The current vertical stabilizer is over-sized merely to provide sufficient control authority for a single-engine abort. With in-line thrust, the tail could be significantly smaller. -REL might want to maintain two completely independent engine systems anyway, but there would be an opportunity for some small cost, complexity and mass savings by having a single engine albeit probably 2X the size in most of its components.-inline thrust seems to offer small advantages in terms of control stability, and the tail-mount nozzle offers greater authority from thrust vectoring, at the cost of differential throttle for yaw control-no issues with exhaust impinging on the airframe (could be a big issue, as we saw way up-thread)-The ducting that runs the length of the vehicle could double as structural members. On the face of it, it seems unwise to have structural members go through such extreme thermal and therefore dimensional transformations, but I also read that SR72 expects to have a “warm” structure, so maybe it’s not mad.-Perhaps the hot piping could be jacketed with a co-axial pipe carrying LH2 forwards, although REL might actually be embarrassed to field such a low-tech brute-force HX. It’d be a poor substitute for the current design’s enthalpy-recovery HX. -Could the bypass burners’ exhaust be ducted out the canard’s tips? Perhaps the canard could be raked more strongly in order to reduce the amount of kinetic energy lost by redirecting the bypass air sideways. -All this ducting might force a change in the OML, with presumably a slightly wider fuselage at the base, making Skylon look more like a Dreamchaser and less like an F-104.-There have been some experiments with drag-reduction via venting small amounts of air through tiny holes all over an airframe. Perhaps an alternate use for bypass air, but not a system that would play well with a TPS.
Note in comparing the above manuals that the current D1 finally gets to a full 17mt "payload" by several fudges such as lower orbital altitude and mass capability in that the vehicle is now capable of handling less than 20mt overall with a specification of a maximum of 17mt to LEO (600km as opposed to 800km in the C2) shown.Nothing 'wrong' with this in any way it's refinement of the Skylon design, but it does point out the issues being discussed about SSTO vehicles.
REL put the engines where they did because they are engine designers and not actually airframe designers.
issues with exhaust impinging on the airframe (could be a big issue, as we saw way up-thread)
With sufficient additional LH2 could the bypass air be utilized TAN style to enable the main nozzles’ expansion ratio to be tuned closer to vacuum optimum?
I understood the preferred method was self ferry.
it's actually the opposite; The length is decreased with a smaller propellant load
Quote from: 93143 on 03/10/2016 10:41 pmQuote from: RanulfC on 03/10/2016 02:24 pmQuote from: francesco nicoli on 03/08/2016 07:46 pmI still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures.If we had actual performance figures, there would be no room for said conversation. The whole point is that we don't; the viability of the design is not known yet and depends on how close they can get to their estimates. The question is: how much margin for error in those estimates do they have? If my math is right, it seems they have quite a bit...If their math is correct then your math is probably correct to their estimates... Which still doesn't eliminate the possibility that everyone's math isn't going to be met by actual performance. Doubtful but the chance is non-zero to a significant degree.
Quote from: RanulfC on 03/10/2016 02:24 pmQuote from: francesco nicoli on 03/08/2016 07:46 pmI still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures.If we had actual performance figures, there would be no room for said conversation. The whole point is that we don't; the viability of the design is not known yet and depends on how close they can get to their estimates. The question is: how much margin for error in those estimates do they have? If my math is right, it seems they have quite a bit...
Quote from: francesco nicoli on 03/08/2016 07:46 pmI still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.You need the numbers, the ACTUAL numbers to base such a conversation on. The numbers provided by 93143 are the best estimates available from the estimates and assumptions that REL has done so far which is all well and good. But they are still not actual performance figures.
I still see no reply to the very informative post of 93143. Any one with better numbers? let's have a polite discussion on how much off the design must be not to deliver. We all want to see the calculations of those claiming the margins are really small.
Quote from: Paul451 on 03/17/2016 03:11 amQuote from: RanulfC on 03/16/2016 09:12 pmbut dropping off the excess mass of the booster stage and continuing the mission profile with a more efficient second stage that is fully reusable is as valid an assumption as not.If you're using SABRE, then you've got that backwards. You'd have a reusable first stage (the Skylon-derivative), with an expendable all-rocket, vacuum-optimized upper-stage.No reason to assume it would be expended
I wouldn't expect a reduced SABRE propellant load. I'd expect the second stage to be pushed out of the cargo bay at around 200km altitude during a ballistic coast, doing around 6km/s
I wasn't calculating the performance of the vehicle. I was calculating how badly wrong REL's estimates would have to be to kill their idea completely.
The issue isn't whether Skylon is possible, but whether it's practical. We don't need another unaffordable launcher.
It doesn't take much to blow out the already-extraordinary design costs. Nor to blow out the ops costs.
Er, and "upper-stage" has ALWAYS been implicit in the design of Skylon you DO understand that right? Skylon is ONLY capable of reaching LEO so it would have been useless for it's "designed" job of delivering commercial satellites if it could not put them into the proper orbit(s) as required.
Quote from: RanulfC on 03/22/2016 03:39 pmThe required delta-v from LEO (800km with the C2 or 600km for the D1) was always implied to be part of the "payload" mass to LEO carried by the Skylon. I think that was always one of the biggest confusions.RandyWhich in-turn leads to a smaller true payload. Shuttle also had the capability to have an extra upper stage as payload capability, if I'm reading this thread right.
A D-21 shape isn't really that bad of a basis for starting, it's been suggested for 2 or 3 combined cycle demonstrators that I can recall
Skylon has been compared to being a hypersonic/orbital airship at times and really the current wing size is enough for fully loaded take off so getting back down is going to be rather "fluffy" in any case
One thing to keep in mind is the Skylon basic shape is designed to be as easy as possible to fabricate. Avoiding complex shapes or curves in favor of simple (and well understood) rounded tanks. Once you start trying to wrap tankage around a single engine you have to move towards a more complex design which complicates fabrication and increases cost etc.
I was pointing out that the Air Force (and hence AFRL) happens to like the ability to move both the launch point AND the launcher around to keep Op-For guessing as much as possible. You can't do that with a ground launch system and even most air-launch systems have issues due to range requirements and restrictions. (Yes in fact they can and do often apply to the military as well, especially in peace-time) SABRE "air-breath's" so that's probably part of what AFRL is considering.