The IIS Express

[craigmac]

<font color="red">The whole concept of aerobraking is to use what is naturally available to save weight. Hauling any kind of reaction mass into orbit in order to get back down is to be avoided. If you are in orbit around the Moon, or Mercury, then you must cancel all of your velocity with rocket power. Earth and Mars (Venus, too, if anyone cares,) both have adequate atmospheres for aerobraking.</font><br /><br />That is not necessarily true. With the exception of reentry at a 20-40 degree angle; and depending on the shape of the craft, we really don’t have a real aerobraking technology. Compressed air along w/ some other tricks could be the "proof in the pudding"…<br />

 

[halman]

CraigMac,<br /><br />I am not sure what you mean when you say that we "do not have aerobraking technology." If we are slowing our vehicle down with atmospheric resistance, isn't that aerobraking? <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[craigmac]

Technically no. If NASA could stop the craft in mid-air and avoid heat friction altogether; don't you think they would do just that?

 

[halman]

CraigMac,<br /><br />Perhaps we are arguing about semantics. I consider aerobraking to be any use of an atmosphere to slow a space vehicle down, irregardless if it is re-entry or a capture maneuver. Reducing the danger of aerobraking is what I am interested in with my idea of a 'space anchor.' <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[craigmac]

I like the anchor idea. Having a tethered anchor could definitely reduce the friction of retry. How about some other ideas of reducing the speed, or at least absorbing the heat friction? What about fitting the shuttle upgrade w/ some type of cooling system like frozen CO2 to shield its outer layer of skin?

 

[halman]

Craig_Mac,<br /><br />Every pound of vehicle is begrudged, to wring the utmost from the engines. The current Thermal Protection System is an absolute marvel of materials engineering. I have no idea what the total weight of the TPS is, but I am confident that it is not a large fraction of the vehicle mass. Piping a super-cold material under the areas most prone to heating is likely to require considerable weight, unless the piping can be consolidated into the structural elements.<br /><br />The space anchor and tether reel could probably be brought in at around 1500 to 2500 pounds, if the carbon nanotube technology pans out. The Reaction Control System for the anchor sled might be a problem, though. I have no idea how much reation mass is required for positive control through the plasma phase. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[craigmac]

The original mercury capsules used retro-rockets during re-entry, why doesn't the shuttle use this procedure anymore?

 

[halman]

Craig_Mac,<br /><br />The original Mercury capsules had a rocket pack strapped over the heat shield which provided the thrust to leave orbit and return to Earth. Every vehicle which returns to Earth from orbit must cancel some of its velocity around the planet to break out of orbit. The space shuttle uses the Orbital Maneuvering System, which consists of the two small engines mounted above the main engines on the space shuttle.<br /><br />The shuttle is moved so the it is facing the way that it came, and then the rockets are fired at precisely the correct time to begin a descent which will end at given point. Then the shuttle is turned around, facing forward again, and the nose lifted slightly. This is the attitude that the shuttle will be in when the atmosphere begins to slow it down. The atmosphere is used to slow the shuttle from 18,000 miles per hour down to about 1,200 mph. In the process, the tiles on the bottom of the wings and along the leading edges absorb an incredible amount of heat.<br /><br />I am trying to figure out a way to use the atmosphere to slow down without getting the vehicle really hot. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[craigmac]

<font color="orange">halman-<br />Every vehicle which returns to Earth from orbit must cancel some of its velocity around the planet to break out of orbit.</font><br /><br />This my point are we doing all that we can; as far as the orbital mechanics are concerned, when dealing w/ reducing the velocity?<br />

 

[spacester]

Well, I have had an idea for a few years on the heat of re-entry thing. <br /><br />The Shuttle nudges out of orbit with just a few meters per second deltaV. You have to scrub around 8000 meters per second. What if you scrubbed a few hundred or even 2000 meters per second for re-entry?<br /><br />Well the first and most obvious answer is that you could have brought up payload instead of that fuel. Yeah, yeah yeah, I know that, but bear with me here, let's look to the future not the past, OK? What if you took on de-orbit propellant after you achieve orbit? OK, you can see how that would really drop the heat of re-entry, right? You go to a space station, "re-fuel", and when you return, you do a great big burn and come in much cooler.<br /><br />To which the obvious but quite correct and pointed objection is: <i>What if the mission to take on de-orbit propellant fails? What if it turns out you cannot "refuel"? Are you saying you needed that fuel to land safely?</i><br /><br />Answer: No, but if I get the Astronauts and tourists to the space station, it enables low-maintenance operations. The folks can come back in "cool mode." <br /><br />You are quite correct that manned space flight operations need continuous abort capability. Fine; if I get to orbit but cannot add deltaV capability, I need to come back in "hot mode", that's all. No big deal. Everyone on board knows that it is a possibility. Their trip was not successful (space but not space station) but they end up fine.<br /><br />The TPS would be designed to support this: You would use a lot of thermal blankets over a fail-safe titanium (X-33 derived) replaceable tile system. If you come back cool, the thermal blankets are 90% untouched and good to go. You would have some replaceable blankets in certain areas perhaps. Quick inspection and changeover for the next flight as long as you got to the space station and got your fuel and oxidizer.<br /><br />Now, if you have to come in at full orbital velocity, the blankets become abla <div class="Discussion_UserSignature"> </div>

 

[halman]

spacester,<br /><br />So far, I have not gotten much feedback on my idea of trailing an 'anchor' on a tether, so that the 'anchor' does the aerobraking, and pulls the orbiter into the atmosphere slowly. The 'anchor', which is really an inverted lifting body, would get hot, while transmitting the velocity change to the orbiter via the tether. By using a remote piloting system, the 'anchor' can be 'flown' to maximize the energy dissipation without overstressing the tether. Because the 'anchor' is an unmanned vehicle, it can get very hot without undesirable consequences. Also, because the 'anchor' would be a thin sheet of material held rigid by internal air pressure, perhaps, the heat transfer and dissipation would be rapid.<br /><br />Short of carting several thousand pounds (or would it be million?) of propellant into orbit for the express purpose of deorbiting, I can not think of another way of losing orbital velocity without exposing the vehicle to temperatures in the plasma range. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[spacester]

halman,<br /><br />Your idea requires unobtainium at this point in time, correct?<br /><br />I'm sorry, but I focus my efforts on the very near term. What can we do NOW to get this space age in gear? That is the question I work on; not what we can eventually achieve in spacetopia, what about NOW?<br /><br />So I do sincerely apologize for the lack of feedback, but it's as simple as that. I spent the time to look at all the future tech I could, but that was two years ago when I had the time to do detailed research. Time constraints and inclination lead me to focus on the here and now, so I'm just not gonna spend time on your ballute idea.<br /><br />I hope you understand and will return the favor you sought and consider and react to my idea. It's something BlueOrigin or whoever could start designing NOW.<br /> <div class="Discussion_UserSignature"> </div>

 

[halman]

shuttle_guy,<br /><br />Thank you for letting me know that I am not crazy! I am a little sad that I am not the original inventer, but, oh well. The whole idea is dependant upon materials science succeding with carbon nanotubes, so that a tether sevral miles long does not weigh several tons. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[halman]

spacester,<br /><br />I understand your reluctance to exam ideas which are not immediately useful. I feel the same way. However, all the talk about carbon nanotube technology, Earth Orbiting Elevators, and such got me to thinking about what we could do with a tether that is strong and light. Reducing risk during deorbiting was the first thing which came to mind.<br /><br />If such a concept were to be implemented, a lot of testing and development would be required. So, even though the idea is not feasible at the moment, preparing for the time when it is would be worthwhile, I thought.<br /><br />I am not sure I know which idea you are referring to in your post, when you asked for a reaction. Please elucidate. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[spacester]

<font color="yellow">I am not sure I know which idea you are referring to in your post, when you asked for a reaction. Please elucidate. </font><br /><br />Um, the idea outlined in my post just preceeding my most recent one. Before this one, that is.<br /><br />A space taxi that would come back in either cool mode - having taking on de-orbit propellant, presumably from a space station - or hot mode, having failed to get the additional prop.<br /><br />If you come back in cool mode, you can turn right back around and fly in a day or two. If you come back in hot mode, you have some refurbishing to do.<br /><br />The idea is to <br />1) Achieve airliner type operations and have an ultra-safe return the vast majority of the time, and a merely safe return occasionally;<br /><br />2) Create a market for de-orbit propellant <div class="Discussion_UserSignature"> </div>

 

[halman]

spacester,<br /><br />Uh, oh, yeah. Sorry!<br /><br />You are certainly on the right track, as far as diminishing the hazards of de-orbiting into an atmosphere. I think that the concept of multiple layers of Thermal Protection System merits examination on its own for immediate use.<br /><br />I am certain that we eventually will have sources of propellant available to use for large delta V deorbit burns, the question is when? And will the cost be justified in terms of increased safety? After all, the shuttle's TPS has proven to be remarkably robust, considering it is a first attempt at a reusable heat sheild. (I know, I know, it is very high maintenance, but I still think that we did good for the times.) We also must bear in mind that canceling all of a vehicle's velocity results in a fall straight down, which can result in considerable velocity as well.<br /><br />I am hoping that things move so quickly to make a space elevator possible that these discussions will be moot, but I am a dreamer. Your idea is superior if a source of propellant is available, and, until then, we can try mine. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[marcel_leonard]

<font color="yellow">Create a market for de-orbit propellant</font><br /><br />Do you have any links on the subject of de-orbit propellant, or coolant? <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[spacester]

Nope, sorry. I found precious little a few years ago when I came up with the concept. There's nothing new under the sun they say, so I was surprised that it seemed to be an actual new idea. Someone else <i>must</i> have thought of this before . . . <br /><br />The idea does not apply to the current Space Shuttle . . . <div class="Discussion_UserSignature"> </div>

 

[marcel_leonard]

Here is something I found. <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[craigmac]

<font color="yellow">najaB-<br />marcel, 10 km/sec = 22000+ mph </font><br /><br />just out of curiousity do we currently have any engine technology other than rockets that can reach escape velocities of 25K+ m/h?<br /><br />

 

[dan_casale]

It is possible with a harp type gun. But a rocket is still required because the orbit is too eliptic and will hit the ground again.

 

[marcel_leonard]

I was thinking about the F-18 Hornet's weapons configuration. Imagine a two stage delivery system where a large jet launches a smaller rocket powered orbiter. I think we have the technology in place today to launch the current Atlantis orbiter in this fashion... <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>

 

[fatjoe]

This would probably work best with some type of scramjet/plasma propulsion engine....

 

[craigmac]

<font color="yellow">Dan_Casale-<br />It is possible with a harp type gun. But a rocket is still required because the orbit is too eliptic and will hit the ground again. <br /></font><br /><br />I you referring to the so-called super gun which in theory could launch a satillite into orbit?

 

[marcel_leonard]

Okay point well take; now how about a slightly larger heavy lift Arianspace booster w/ a top payload caption of a modified European Hopper version of a smaller Orbiter? <div class="Discussion_UserSignature"> "A mind is a terrible thing to waste..." </div>