good question.I would take a look at the launchpads in baikonur, they have built them onto an artificial rim, so the flames can blast away in 3 directions.......
A flame pit won't be required. I'm sure the MCT design will take into account the lower gravity requiring lower thrust and the heat from the exhaust. It won't be nearly as bad as taking off from Earth, requiring less than half the delta V to get to low orbit. ......
......I have also often wondered if it would be possible to have the cargo at ground level to avoid any cranes and the rockets higher up. I guess this implies a mushroom like shape: the top is the heat shield (which might deflate for launch), the rockets are around the rim, the stalk is the cargo which is left behind on launch. Perhaps the rockets could gimbal out a bit to avoid their thrust squashing the cargo section on launch.
Quote from: KelvinZero on 05/04/2015 11:25 pm......I have also often wondered if it would be possible to have the cargo at ground level to avoid any cranes and the rockets higher up. I guess this implies a mushroom like shape: the top is the heat shield (which might deflate for launch), the rockets are around the rim, the stalk is the cargo which is left behind on launch. Perhaps the rockets could gimbal out a bit to avoid their thrust squashing the cargo section on launch. I have also thought about the process of unloading a vertically landed cargo rocket. Perhaps one solution will be related to the facilities required at a launch pad, as follows:1) First, assume that MCT will be a larger version of Dragon 2 – extended. The mushroom heat shield that you suggest could be a contracting umbrella-like extension of a bi-conic or triconic nose cone. The cargo version lands vertically using retro-propulsion and is employed by the expedition sponsor to deliver materials and equipment to Mars in advance of the first humans.2) MCT will require a method for transporting itself to a launch pad, fueling up, and launching. On Earth SpaceX already employs a transporter-erector-launcher (TEL) to accomplish those functions. A Mars version of this (MTEL) could be designed for an additional task, which is to facilitate unloading cargo.3) MTEL must be designed and built in sections so that it can be compactly loaded into the cargo bay of the MCT. It will be larger than MCT so may require two MCT delivery trips.4) MTEL must be simple to assemble because robots will put it put together. The robots could ride along with the MTEL sections or they could be designed as an integral part of the MTEL system.5) MTEL should be the first cargo delivered to Mars. As such, it must be self-unloading because there will be no other equipment to help unload (an interesting additional problem).6) On Earth, a TEL attaches to a rocket and carries it to a launch pad. MTEL could drive (itself) to a MCT that just landed and attach to it. It could then lower MCT from a vertical to horizontal position. Now it is much closer to the ground for unloading.7) If you want to unload even closer to the ground then MTEL should drive MCT alongside an outcrop or ledge of convenient height from the ground, which happens to be the same height as the hatch. Then a short ramp can extend straight across from the cargo bay hatch to the ledge. A forklift could drive cargo packages from the cargo bay directly onto Mars’ surface.
Mars gravity is 0.38 g. Atmospheric pressure is less than 1% of Earth's atmosphere. The MCT won't need as much thrust as a rocket of the same mass on Earth and the rocket exhaust is going to quickly spread away. Of course they are going to need berms to block debris from hitting whatever is near the launch pad. I guess you could build a flame trench instead of berms, but that would be more difficult.FOD is foreign object debris.
........Why move the MCT to a launch pad? Launch it from the same pad it landed on.
Quote from: RonM on 05/05/2015 08:06 pm........Why move the MCT to a launch pad? Launch it from the same pad it landed on.As I have learned, it will be necessary to protect people, supplies and equipment from FOD thrown away from the launch or landing pad by the rocket exhaust. The landing pad will be just a pad, perhaps located in a crater to contain the FOD. The launch pad will be a platform with a (sophisticated) hole in the middle to allow the plume to exhaust into a crater. See reply #12.
If you build that sophisticated launch pad, why aren't you landing onto it? Do you expect the traffic to be so heavy that you couldn't afford the time to land, unload, refuel and take off? Now, that doesn't mean I wouldn't have an extra pad or two in case of something taking the sophisticated one out for some reason, but before you could build this sophisticated launch pad you would have had to accurately land a few with no pads, then several on the first unsophisticated pad. However I don't see the hole being in the middle unless it is for a 2nd cargo lander model after the base is established, I don't see the initial ones being able to land on un prepared locations without having their engines canted out to protect the engines from FOD during landing.[edit] Also engines canted out so initial landings don't disrupt stability of surface under the lander so that it stays vertical and does not fall over [/edit]
I can certainly understand the desirability of landing and launching on the same pad. We ought to see if we could make that work. So I have some questions about your question.First, refueling prior to launch. If we put the (ISRU) LOX and methane producing equipment right next to the pad then it is just a matter of attaching a hose from one to the other prior to launch. But would this procedure not introduce a level of danger to the ISRU equipment during landing?
As you may see in Reply #12 I would prefer to carry around an empty MCT using a Mars-adapted TEL that could also be used to unload cargo. If we need to transport wheeled tankers from Earth to Mars before we can launch one NCT back to Earth we may be extending the equipment pre-deployment period before the first humans arrive.In another instance, if we tried to carry the MCT to the fuel loading station and then to the L/L pad then MCT would be different from other rocket vehicles in being able to be carried around while it is full of fuel (not likely).
.........I don't see having the ISRU equipment near the pads but I think it would be a lot less infrastructure cost to bury insulated piping in two trenches that runs from outside the crater to the inside. I am not thinking this pad happens until we have had at least a dozen cargo flights land and it will be for when we have set up a permanent (but expandable) ISRU facility.So even with the low Mars gravity you are talking about a road that has to support say 23t of empty MCT 60t adjusted for 0.38g at mars and I can't imagine the TEL weighing less than the MCT so we need something that is about twice the rated capacity of your average gravel road. I believe digging 2km trenchs for the propellant pipes will be cheaper in terms of total mass and energy required.