Wheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.
Quote from: Lobo on 04/21/2015 11:32 pmAgreed. So you resolve this by not having the engines in the heat shield at all. That gets back to the biconic aeroshell with engines at the aft. Essentially a wingless Spaceshuttle that lands on it's SSME's. Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given. The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly.
Agreed. So you resolve this by not having the engines in the heat shield at all. That gets back to the biconic aeroshell with engines at the aft. Essentially a wingless Spaceshuttle that lands on it's SSME's.
I also think SpaceX should develop their Raptor engine like the BE-3 that can throttle from 30% to 110%. That would make for easier landing on earth or Mars.
Sorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs).
This is why a vehicle or vehicles of some sort should be landed on the first lander to take people and supplies over to wherever robotic equipment has landed to set up housing. That being said, a 100 ton lander on Mars would weigh 40 tons, but that is still quite heavy. I think some type of flat plains area should be used for landers.
Quote from: Impaler on 04/23/2015 02:42 amSorry about that, thought you were describing a alternative vehicle from the one in your sketches, a bi-conic that lands vertically on it's tail indeed has no heat-shield penetration issues (other then landing legs). Ahhh...no problem.The legs don't necessarily have to protrude through the side heat shield. I did post one image showing that, but as I said in my reply to Hyperion, there's other ways around it. In fact, Hyperion posted a couple of pics illustrating those alternatives.Pic 1: shows legs deploying through the side TPS.Pic 2: Extendable jack-stand like legs that come pretty much straight down. The H/W ratio of MCT would be a factor in that to make sure it's stance was wide enough.Pic 3: blisters or nacels on the sides which legs could exend out and even more of an angle, for a wider stance. (Again, I almost think this picture is a biconid with the TPS on the other side. The dorsal side is shown to us. That MPS on the bottom just doesn't look set of for atmospheric entry that way.
You are missing that the MCT will probably be a two stage system.
Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.
A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.
Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.The MCT is divided into 6 Floors from bottom to top with the following characteristics:| Floor | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) ||-----------------------|-------------|------------------|--------------|------------------|-----------|| Upressurized Cargo | 2.5 | 95 | 383 | 177, 1902 | || Habitat | 2 | 95 | 257 | 146, 1577 | || Pressurized Cargo | 2 | 95 | 216 | 124, 1339 | || Systems | 1.5 | 95 | 138 | 104, 1121 | || LOX | 4.6 | 97 | 309 | N/A | 361 || CH4 | 12.4 | 97 | 258 | N/A | 112 |MCT Empty Mass = 65 MTCargo <= 100 MTTotal Fuel = 473 MT
MCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.
Here is my hypothetical MCT design based on the constraint of a 225 MT Fully Reusable BFR.I also disagree about the two stage system. Inflatable tanks in the cargo hold are also not required.Tanks above cargo gives the best layout and CG for landing. So I have chosen it believing the plumbing problem will be solved. If the engines are side mounted, It may even be easier.A crew MCT will not be able to get 100 MT of cargo to Mars. Crew support equipment and systems will subtract from the available 100 MT.Dragon derived 15 m capsule with 15 degree side-walls. Capsule is 25 m tall not including the heat shield hemisphere. Top diameter dome 1.6 m across.The MCT is divided into 6 Floors from bottom to top with the following characteristics:| Floor | Height (m) | Usable Pct (%) |Volume (m3) | Area (m2),(ft2) | Fuel (MT) ||-----------------------|-------------|------------------|--------------|------------------|-----------|| Upressurized Cargo | 2.5 | 95 | 383 | 177, 1902 | || Habitat | 2 | 95 | 257 | 146, 1577 | || Pressurized Cargo | 2 | 95 | 216 | 124, 1339 | || Systems | 1.5 | 95 | 138 | 104, 1121 | || LOX | 4.6 | 97 | 309 | N/A | 361 || CH4 | 12.4 | 97 | 258 | N/A | 112 |MCT Empty Mass = 65 MTCargo <= 100 MTTotal Fuel = 473 MTMCT Launches with cargo and crew and 60 MT of fuel to awaiting BFR Depot to fully fuel with additional 400 MT of fuel. Performs TMI and EDL at Mars with a DV of 5036 m/s. Each Mars MCT will only require 2 BFR Tankers.MCT Refuels on Mars utilizing 473 MT of ISRU fuel and returns to Earth with up to 10 MT of crew/cargo with a DV 7405 m/s.Distributed MCT engines require a minimum thrust around 50 MT and 250 MT Maximum.
Quote from: Hyperion5 on 04/22/2015 03:16 amQuote from: Lobo on 04/21/2015 11:32 pmAgreed. So you resolve this by not having the engines in the heat shield at all. That gets back to the biconic aeroshell with engines at the aft. Essentially a wingless Spaceshuttle that lands on it's SSME's. Given the number of designs with engines embedded behind deployable heat shield doors, I would think the "wingless" Space Shuttle design is far from given. The simplicity of landing with a Dragon-style vertical lander on Mars is not something to be given up lightly. Well, we can't say anything is a given or not given until SpaceX announces something official. ;-)But some of these designed you posted pictures of are comparing apples to Oranges, or are some artist's fiction. None of the addresses both Issues MCT will have to. 1) To be fully reusable, rather than 1-shot.2) To get itself back off the surface after it lands. which introduces a lot of issues like a large high performance engine needed, rather than just some low ISP landing thrusters. All Mars Landers to date had those in one form or another, but none of them had to get back up and back through TEI. Heck Dragon could land on Mars and it's a capsule. It just can't get itself back to Earth. So that's a very different issue that makes capsule designs much more problematic.
Image #1: I can't see where the heat shield is on this. The whole bottom is shaded, and I can't see the other side. But this almost looks like the heat shield is on the other side, given the odd shape of it's bottom. This looke more like a "wingless shuttle" than a capsule.Image #2: Again, where's the heat shield. Is it on the other side? Is this a wingless shuttle too? Or did it have a jettisonable heatshield on the bottom. If so, then it's not reusable like MCT will be. MCT won't [likely] be jettisoning it's heat shield. Otherwise it couldn't land back on earth. If it were to some how be able to brake itself into LEO (how?) it would need a new heatshield brought up and attached in LEO. Which seems...unnecessarily complex.Image #3: Ok...so what was protecting thos engines during entry? Did it have a portion of the heat sheild jettison? And if so, see my comments about that on Image #2.Image #4: That image is from "Voyage" by Stephen Baxter. Great book! I highly recommend it. That is the Mars lander Baxter put in his novel. But that is an expendable two-stage lander like the LEM. It had a conventional capsule shaped descent module (described by Baxter that it was chosen over other more advanced bionic designs because of it's heritage and that they "know" it would survive, where biconics hadn't been tried before....and if they are going to risk Humans on the very first trip (there was only funding for just one manned trip to Mars) they wanted to go with a proven and stable design. It's top and central core were the ascent module. It blasted off from the capsule bottom back to LMO for rendezvous with the MTV. It was really an Apollo redux, but with a lander descent module that could withstand atmospheric entery. Again, this lander can't get itself off the surface whole, only the ascent module portion could get back to LMO, just like the Apollo LEM. The ascent module engines were protected within the MEV like the LEM AM engine was, and the descent module portion was destoyed when the ascent module blasted off. The whole lander couldn't take back off again with it's landing thrusters (even if it could have been refueled) and it wasn't reusable. A good safe one shot design but it would share little in common with what MCT is supposed to do.
A biconic has a lot of advantage over a capsule. It has a large surface area, so it's TPS doesn't have to be quite as thick and it's terminal velocity is slower. The engines are in the afte and not exposed to the atmospheric entry, or the supersonic terminal velocity slip stream like those of a capsule. Although it's not impossible to have doors in your heat shield...the shuttle, X-37B, and Dreamchaser do after all for their landing gear...having a large main engine with a large nozzle which gimbals is more problematic than landing gear. Assuming such a capsule design would have Superdraco like landing thrusters, and then one or more Raptors tucked behind the heat shield, then you have to retract those doors (that can be done on the ground if there are separate side wall landing thrusters) but then you need enough room for those main engines to gimbal, so the doors need to be much wider than the nozzles. and then those doors need to close again prior to Earth EDL or else you have the Columbia all over again. That's on top of landing gear which will need to come through the heat shield as well. So there will need to be several doors in the heat shield.
I'm sure it -could- be made to work. But why force it when you don't have to? A biconic "wingless shuttle" design solves all of that. You can even get around needing to have legs extend through the heat shield on its' side in various ways, include just having jackstand like legs come straight down from the MPS (if the diameter is wide enogh to be stable, similar to your pictures #2) or you could have blisters around the MPS housing the legs. With a shape not unlike your image 1. The legs could fold out from those blisters to give MCT a wider stance on the surface.
Because while there are vehicles which have had doors in their TPS, there's never been one that's had to close those doors again prior to anther reentry. They open once after atmospheric entry and that's it. They're closed on the ground an checked out before sent back up. So avoiding that dynamic portion of the heat shield and making it all static/passive increases mission safety.
It would be interesting if Lobo or others could do the same volume/mass estimate on the combined 2nd-stage style MCT concept.
We (ok at least me) are/is talking about protecting the craft that is landing from damage to it's engine/heathshield from impacts with 1cm sized gravel moving as much as 1.2km/s - one of the reasons why engines might be mounted on the outside and have a gimbal range from 0° from the vertical to 30° from the vertical (pointing out). That angling, and the fact that the engines are on the outer radius, also protects the landing site from being destabilized under the landing craft so that it can't take off without major earth moving, hoisting, etc.
Yes, but that will only be done if more traffic is going there, so it will probably be the 2nd or later MCT to that site location that caries the earth moving equipment to do that. My point is that I think the MCT has to be designed (and operated) to minimize the risks to the MCT and to anything already on the ground. Angling the engines outward, having them outside of the radius of the craft, and ensuring that landing orientation of engines puts already landed equipment at the least risk is needed before landing pads are built up at a site that will experience significant future traffic.
I would seem that a small, deep crater with the center peak flattened out would likely be the best choice for this sort of launch pit.
Quote from: Lars-J on 04/24/2015 08:29 pmWheels are harder than it seems on Mars - or any near vacuum body. I don't think it is realistic that massive landers massing 100+ tonnes can be supported by wheels. Just look at how the MSL wheels are surviving. The lander will also be VERY heavy when fully loaded with propellants for departure.No, IMO you need to plan on landing them where you need them. If you can't do precision landing yet, you probably should not start a colony.Nobody jacks up a fully loaded aircraft why would you assume they do so for an MCT? At landing it will be almost empty of propellants so its FAR from as heavy as you seem to be thinking."Landed where you need them?" Nice idea but how ACCURATE does that have to be? You "need" not to put the colony structure in danger, nor other already landed MCTs. 2km? 5km?