Is there any way that the shuttle orbiter can reenter the atmosphere and land in a more gradual manner so that there is less problem with heat, i.e. take a longer less steeper path during the descent? Is it aerodynamically possible?<br /><br />It's my understanding that the orbiter reentry, from orbit to runway, takes about an hour. What if the orbiter could glide and spiral around in the atmosphere for a longer time, like several hours, before finally gliding down to the runway? I would think that if the orbiter, or any future vehicle, could loiter in the atmosphere and descend slower and more gradually that there would be less problems with heat.
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The current trajectory is pretty well optimized for minimizing heating. It attempts to bleed off as much energy as it possibly can, as high up as it can, to minimize heating.<br /><br />Note that reentry is a trade between peak heating, and the duration of the heating profile. Some configurations of reentry vehicles can live with quite high peak heating, as long as heating overall doesn't last too long. <br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher</p> </div>
The biggest problem is from orbit to the upper atmosphere the Shuttle is basically falling. Even if you reduced the speed to zero in orbit the acceleration from 100 miles to 400,000 feet would bring it right back up. <br /><br />SS-1 still needed some protection, even though it peaked at a slow speed the descent increased it's speed enough to cause problems. The only real alternative would be like in the old movies. Engines firing to moderate the descent to a landing. The problem is where to put all that propellant, it would take pretty much the same amount of propellant to come down as to go up. <div class="Discussion_UserSignature"> </div>
The Shuttle is a challange because heating is concentrated on the sharp leading edges. There are two ways to reduce peak heating; one is to simply increase the area over which the heating is spread; this was why Mercury was designed to re-enter blunt end first. With a large deployable or even inflatable metal cone as a heat shield, a craft could re-enter without requiring a ceramic shield. The second approach is to raise the hypersonic lift-to-drag ratio with a "waverider" or "compression lift" type configuration in which the deceleration shock wave provides lift by pressure on a long curved wing. This yields an elegant-looking craft that has enough lift to make a very slow descent, and would be ideal for a real fully resuable shuttle, but unfortunately is a challange to build. <br /><br />Although it is not reusable and permits little lift, the Apollo heat shield, a metal honeycomb filled with ablaitive ceramic, is simple, rugged, and not very expensive.
"Although it is not reusable"<br /><br />Actually, the Apollo heat shield was so overbuilt that it was in all likelyhood good for several uses...<br /><br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher</p> </div>
yoda9999:<br />Is there any way that the shuttle orbiter can reenter the atmosphere and land in a more gradual manner so that there is less problem with heat...<br /><br />Me:<br />Not possible because the design would become impractical. The shuttle is essentially falling into the earths atmosphere once the OMS engines fire and cause it to slow down enough to cause the fall to begin.<br /><br />It could slow its descent down with ungodly amounts of propellant which is the impractical part. The shuttle uses the atmosphere as a brake. The heating is a manageable problem as the thermal protection tiles have always done their jobs well. As has the RCC. The problem that needed more attention was how to keep the orbiter from being struck by debris during ascent and at this late stage in the game. They have done about all they can without major redesigns that would force a major grounding that would in turn, probably end the shuttle program. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
While the shuttle is "falling" after the OMS engines fire,<br />that fall is not at 1 g. To get that rate of fall, the OMS<br />engines would not to stop all of the horizontal velocity.<br /><br />Therefore the shuttle would enter the atmosphere<br />relatively gradually compared to say, a suborbital <br />rocket like spaceship one. However, unlike spaceship<br />one, the shuttle has a significant horizontal component<br />to dissipate.
At the risk of being pedantic (I know you know all of this, but others might not), the shuttle is in fact *always* accelerating towards the center of the Earth, with an acceleration equal to the local value of "g".<br /><br />The shuttle is in fact always in free fall.<br /><br />What keeps it in orbit is that it is going around the Earth in a trajectory that is consistent with the "prescription" for circular motion, i.e.<br /><br />Fg = mv^2/r<br /><br />Now, some people like to look at that as a "centrifugal force", but the reality is that there is no such beast, it is a product of looking at the problem in a non-inertial reference frame. (Sorry for the little tangent and pun there)<br /><br />Now, when the shuttle fires its thrusters, it changes its "v" such that it is not longer consistent with the prescription for an orbit at that altitude.<br /><br />Strictly speaking, the shuttle does not fall out of orbit, it simply lowers its orbital altitude to a point that is within the atmosphere, and uses the atmosphere to do the rest.<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher</p> </div>
Much better description of the process. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
I find myself in DEEP awe of people who are really good at orbital mechanics. <br /><br />There is wild stuff that you can do with orbits - the Soviets put up a satellite some years ago that is in a weird resonance orbit that essentially never decays. Departures from symmetry that make things intractible for my limited brain are their playground....<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything." Admiral Jackie Fisher</p> </div>
Thanks for all the replies and useful information! I think I understand it would take an impractical amount of fuel to land the shuttle without experiencing the intense heat.<br /><br />I was thinking that in the future, a space plane for tourists might require a more controlled re-entry and landing, perhaps like an airplane; tourists being more concerned about safety and comfort. But I guess you still need a heat shield or hear tiles incase the retrorockets fail.
Heat shields of some type will be needed unless or until we develop anti gravity propulsion which might allow slow re-entry. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
yoda9999,<br /><br />Any re-entry maneuver is a carefully calculated angle, because the consequences of too small an angle are just as serious as those of too steep an angle. If the shuttle does not burn the engines long enough, the vehicle will 'skip' off of the atmosphere, returning to space, but not to orbit. This has been done intentionally in the case of the Apollo command modules when returning from the Moon, because their velocity was so high that reducing it before full re-entry was considered vital.<br /><br />Velocity is what it is all about. The same energy that is expended in accelerating the shuttle to 17,500 miles per hour must be dissipated before it can reach the surface of the Earth safely. Aerobraking has long been considered the ideal way to do this, as no propellent is needed, except for the small de-orbit burn. An aerobraking trajectory begins at a fairly small angle of descent, which grows steeper as the vehicle loses velocity. It would require adding velocity to keep the angle from increasing, as velocity is what 'pushes' the vehicle away from the center of gravity. However, this would extend the time period when the vehicle is subjected to high temperatures, due to its travel through a gaseous medium. The only way to avoid those high temperatures is to cancel virtually all of the orbital velocity while still in a vacum, and then to descend vertically with rockets preventing the vehicle from falling faster and faster.<br /><br />I believe that we have mastered the technology of managing the heat involved in re-entry, just as we have mastered (sort of) the technology of accelerating a multi-ton vehicle to thousands of miles per hour. What we need to learn is how to keep management from cutting corners, ignoring problems resulting from changes in practices, and blaming engineering for their own shortcomings. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>
vulture2,<br /><br />I believe that, if you were to examine the heat signiture of the shuttle during re-entry, the area exposed to the highest temperatures is the belly, the bottom of the vehicle. This is because the shuttle is riding a shock wave, which is protecting it from the plasma its passage through the atmosphere creates. That plasma reaches nearly 20,000 degrees Farenheit directly under the shuttle, but the tiles there are only exposed to about 3,000 degrees.<br /><br />The leading edges of the vehicle experience temperatures around 2,500 degrees, but they also are exposed to higher levels of turbulance. It is turbulance which, combined with heat, is dangerous to a vehicle with a compromised thermal protection system. I believe that it was Endeavour which landed safely with a sizable hole in the leading edge of one of the wings, in the same reinforced carbon-carbon panels that are blamed for the loss of Columbia. Endeavour could easily have been lost, a result of the same foam shedding problem which destroyed Columbia. Unfortunately, upper level management at NASA, who were not engineers, from what I understand, choose not to take action after the warning that Endeavour presented. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>
The nose cone and wing are exposed to the highest temperatures, up to 3,000 degrees which is why the RCC is there. The black tiles on the bottom are exposed to up to 2,200 degrees IIRC.<br /><br />I recall Discovery landing in 1985 with a hole burnt into the port wingtip. I didn't realize Endevour suffered the same or similar problem. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
I can think of a loophole, at least in theory. I think. <img src="/images/icons/laugh.gif" /> Two loopholes, actually. I think. 
<br /><br />The Shuttle just *barely* nudges itself out of orbit to begin descent. This of course makes perfect sense because propellant mass in excess of that is lost payload. Yet it leaves the TPS with the job of dealing with the maximum possible orbital energy. Has the option of using just a little bit more de-orbit propellant been studied?<br /><br />I'm sure it has, NASA is not stupid, but I have a 'what if': what if the STS orbiter, for example, used de-orbit mass acquired on-orbit. IOW what if the shuttle loaded up on prop at the ISS? What if you had a 'cheap' way to provide de-orbit propellant mass? In theory – wholly impractical, I'm sure – you could even strap some solid rockets onto the orbiter and come in a lot cooler. That's the first loophole: take on a whole bunch of energy after reaching orbit, and then use that to drop in much cooler.<br /><br />I'm halfway decent when it comes to orbital mechanics, but I'm out of my depth when it comes to DE-orbital dynamics. <br /><br />OK, say you're in a circular orbit, up where the drag is tolerable; been there for days having fun, but it's time to go. You slow down just a tad, this means that you have shifted your orbit, you no longer have the kinetic energy to stay where you are and you're no longer in a circular orbit. As you drop into the gravity well, you trade potential energy for kinetic energy and so you pick up speed. Your de-orbit impulse is very carefully chosen to interface with the atmosphere just as needed.<br /><br />This means you're actually going faster when you really start to feel the air resistance than when you were up there on orbit! So the first step in a standard re-entry is to add speed, thus kinetic energy, thus add to the heat load on the TPS! Is this really the best way to go?<br /><br />Well maybe so, what do I know?<br /><br />Loophole #2: What if you spent enough pro <div class="Discussion_UserSignature"> </div>
<br /><br />The Shuttle just *barely* nudges itself out of orbit to begin descent. This of course makes perfect sense because propellant mass in excess of that is lost payload. Yet it leaves the TPS with the job of dealing with the maximum possible orbital energy. Has the option of using just a little bit more de-orbit propellant been studied?<br /><br />I'm sure it has, NASA is not stupid, but I have a 'what if': what if the STS orbiter, for example, used de-orbit mass acquired on-orbit. IOW what if the shuttle loaded up on prop at the ISS? What if you had a 'cheap' way to provide de-orbit propellant mass? In theory – wholly impractical, I'm sure – you could even strap some solid rockets onto the orbiter and come in a lot cooler. That's the first loophole: take on a whole bunch of energy after reaching orbit, and then use that to drop in much cooler.<br /><br />I'm halfway decent when it comes to orbital mechanics, but I'm out of my depth when it comes to DE-orbital dynamics. <br /><br />OK, say you're in a circular orbit, up where the drag is tolerable; been there for days having fun, but it's time to go. You slow down just a tad, this means that you have shifted your orbit, you no longer have the kinetic energy to stay where you are and you're no longer in a circular orbit. As you drop into the gravity well, you trade potential energy for kinetic energy and so you pick up speed. Your de-orbit impulse is very carefully chosen to interface with the atmosphere just as needed.<br /><br />This means you're actually going faster when you really start to feel the air resistance than when you were up there on orbit! So the first step in a standard re-entry is to add speed, thus kinetic energy, thus add to the heat load on the TPS! Is this really the best way to go?<br /><br />Well maybe so, what do I know?<br /><br />Loophole #2: What if you spent enough pro <div class="Discussion_UserSignature"> </div>Keeping in mind you are burning LOX and LH2, pretty much the most powerful rocket fuels possible, to carry solid rocket technology (drastically less efficent) for this maneuver . . . .<br /><br /><br /><br /><br /><br />How about designing a vehicle with an even higher angle of attack, to stay higher longer, and therefore burnoff more velocity over a longer arc, over a longer time, in thinner air ?<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
Actually the Shuttle OMS's use hydrazine and Nitrogen tetroxide. <br /><br />The Shuttle slows just a couple of hundred mph and maintains that velocity pretty much until it reaches the upper atmosphere at roughly 400,000 feet or 75 miles. Then drag take over. To establish an orbit at say 80 miles would require a fairly hefty increase in speed followed by an even heaftier decrease if the idea is to enter the atmosphere at a much lower speed. You would also be looking at a pretty tight schedule to flip over to a proper re-entry attitude from the third engine burn.<br /><br /> <div class="Discussion_UserSignature"> </div>
Those fuels are used primarially because they are storable. Cryofuels would boil away even in a really good insulated tank before the end of the mission. However, those fuels also do not require an ignition system making the OMS and RCS engines simplier. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>
You may have noticed by now that you have expended quite a bit of energy trying to solve a problem already solved. The shuttle re-entries have already been optimized to the extent practical and possible. Loading up on propellant at the ISS is one example. The shuttle flew missions long before ISS was sent up. Where would propellant have been put then?<br /><br />The solid rockets, where would you mount them and how? The how I'm assuming your picking the SRBs up at ISS. Otherwise, launching with the deadweight of the SRBs means no payload.<br /><br />spacester:<br />Loophole #2: What if you spent enough propellant to re-circularize your orbit just above the part of the atmosphere where you get the desired braking effect? Your initial velocity at the start of the 'aerobraking' would be much less, so the energy would be less. Yes, the circular velocity is higher for the lower orbit, but would still be less than after falling down the well from a higher-energy orbit. I think. I ran the numbers once, wasn't 100% sure on this conclusion, but as I think about the energy thing now, I get the same result. <br /><br />It seems like you would still get a long time at high altitude, to bleed off the energy as high as possible like shuttle does with the big swooping curves. You would still nudge out of orbit, just lower and with less bound energy to dissipate.<br /><br />Me:<br />Seems to me NASA would have studied this before the shuttles first mission and adapted the method for use if it worked as your saying it should. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
Maybe a variation of aerobraking. Enter an elongated orbit and make a few passes through the atmosphere to slow before starting the final descent. Would probably take less propellant. The biggest problem would be carryign enough consumables for the crew, I'm sure it would take a few weeks. <div class="Discussion_UserSignature"> </div>
And enough consumables translates to added mass. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>
The post I was responding too specifically mentioned adding solid rockets to further decel the shuttle for re-entry.<br /><br />Please try to keep up, this is America's <i><b>premier</b></i> space message board.<br /><br /><br /><img src="/images/icons/laugh.gif" /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
I'm sorry I missed that point.<br /><br />I don't think that would be a good idea. <div class="Discussion_UserSignature"> </div>
I didn't like it either.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
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