Re-entry

[owenander]

can reverse thrusters remove atmospheric entry heating?

 

[qso1]

Only if you have an enormous amount of reverse thrust propellant if I understand what your getting at. An amount incredibly impractical at best. Fortunately our spacecraft that require coming back have well designed thermal protection systems. Out of 116 flights, we lost 1 shuttle and that was not even a directly re-entry related problem. There were 33 manned flights (U.S.) prior to shuttle and no loss of mission or life due to thermal protection faults. <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>

 

[owenander]

Mathematically speaking, wouldn't you need the same amount of thrust to re-enter (at a slow/manageable rate) as it took to leave in the first place?

 

[owenander]

Also, assuming you have unlimited amount of fuel, could you technically leave Earth at 1 mph as long as you never stopped gaining altitude?

 

[willpittenger]

Correct. However, by the time you reached the Moon, you would be going fast relative to other objects. You would inheirit all the Earth's speed that it has going around the sun. <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>

 

[qso1]

OwenAnder:<br />Mathematically speaking, wouldn't you need the same amount of thrust to re-enter (at a slow/manageable rate) as it took to leave in the first place?<br /><br />Me:<br />The liftoff and ascent is anything but slow. The shuttle as an example, goes from zero mph to 16,500 mph (ET sep and just prior to OMS 1 burn) in less than 9 minutes. Look at the amount of propellant required to get this DC-9 sized vehicle to orbit. Millions of pounds of solid and liquid propellant that when burned, generates about 7 million pounds of thrust to get 225 to 250 thousand pounds of vehicle, payload, and crew to orbit. Payload and crew account for well below 1% of shuttle total weight BTW.<br /><br />To come back, and do so at a slow manageable rate would require more propellant than what you went out with. Even if it were the same. Your now talking about launching with the boosters and tank the vehicle already has, then you have to carry the deadweight of the propellant and propellant containers needed for the re-entry which in turn means you have to greatly increase the liftoff propellant mass and its at this point that the impracticability begins to emerge.<br /><br />In fact, carrying the dead weight of propellant just for SSTO vehicles such as the Delta Clipper is an engineering problem still beyond the best and brightest engineers the world has to offer. <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>

 

[owenander]

What is SSTO?

 

[qso1]

OwenAnder:<br />Also, assuming you have unlimited amount of fuel, could you technically leave Earth at 1 mph as long as you never stopped gaining altitude?<br /><br />Me:<br />Yes but its not practical or even possible with current technology. Take a look at why rockets stage for example. Why can't rockets carry themselves up in one piece like the Delta Clipper was supposed to have done in the DC-Y version.<br /><br />At liftoff, an SSTO has to carry enough propellant to lift itself to orbit, including the mass of the vehicle still there when most of the propellant is depleted.<br /><br />This is what lead to the concept of staging, or as it was once known, step rockets. Stage one once empty is no longer needed, its just dead weight and in the way of the second stage engines in current rocket designs.<br /><br />Perhaps one day we will find a way to overcome this barrier but for now. Staging rockets and re-entry is the best we have. <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>

 

[qso1]

Sorry, SSTO is an acronym for Single Stage To Orbit.<br /><br />SSTO is the holy grail of aerospace engineers the world over. An idea that has been pursued for decades from concepts such as SASSTO (Saturn Application Single Stage To Orbit) of the 1960s to Delta Clipper (DC-X and DC-Y) of the 1990s. DC-X was a subscale version of the planned operational DC-Y.<br /><br />Delta Clipper was abandoned when the Clinton Admin announced it favored the Lockeed Venture Star which was an SSTO that eventually succummed to technical problems and cancellation long before it was to have flown. <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>

 

[owenander]

So SSTO Would simply be 1 booster basically? instead of having multiple stages?<br /><br />So not only is propulsion the setback for leaving Earth, but also space travel and reentry.<br /><br />Why is there not more financial backing going for research in this area? Or just pull an X prize and give out $10 mil for the first team to develop new technologies (if they have already link me).

 

[willpittenger]

The only rocket to even reach the drawing board (as far as I know) that could do what you are talking about is the DeltaClipper. Actually, though, the version in question was a follow on to the DC-Y, which was cancelled before it was built. What I found is at http://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X. That article details the only version built and flown. I know the DC-X was strictly suborbital. As I recall, the DC-Y was too. <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>

 

[qso1]

OwenAnder:<br />So SSTO Would simply be 1 booster basically? instead of having multiple stages?<br /><br />Me:<br />Correct.<br /><br />OwenAnder:<br />So not only is propulsion the setback for leaving Earth, but also space travel and reentry.<br /><br />Me:<br />Not necessarily. It is a setback to economical access to low orbit but rockets are launched. At one point, Russia had a record 102 launches in one year.<br /><br />Propulsion is a setback for the kind of re-entry your considering and thats just simple laws of physics.<br /><br />OwenAnder:<br />Why is there not more financial backing going for research in this area? Or just pull an X prize and give out $10 mil for the first team to develop new technologies (if they have already link me).<br /><br />Me:<br />Its tough enough for NASA to get adequate funding, let alone the private sector. But it will probably be the private sector that provides us with economical access to low orbit if its possible utilizing todays technology.<br /><br />Most folks are simply not interested in going into space if it involves a lot of cash and it almost always does.<br /><br />The newest technology that has been proven so far is still limited to the laws of physics and the financier was Paul Allen. This technology would be the Rutan/Scaled Composites effort which in 2004, was able to claim the "X" prize.<br /><br />The simple and unfortunate truth is that we will probably need an entirely different kind of technology to do the things your looking at. <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>

 

[owenander]

That's what I'm saying we should be focusing on those new technologies since the limitations of current technologies are so great and let the private sector keep dealing with current technologies (I guess the COTS program does that to some degree).

 

[qso1]

For the private sector, focusing on proven technologies keeps them from becoming disinterested altogether due to the usually high cost of investment in new technologies. There is also the problem of what new technologies are there at this time.<br /><br />Current tech for getting to low orbit, expending chemical propellant to lift mass into space. A relatively small amount of mass at that.<br /><br />Some technologies for propulsion that are promising but only for space applications due to limitations of operating in the atmosphere. This technology is nuclear propulsion and the best tested IIRC is nuclear thermal and nuclear electric. Neither are very useful within the earths atmosphere. Thermal due to radioactive waste concerns and electric due to it being a steady state kind of propulsion that slowly builds to achieve the right velocity.<br /><br />The electric variety does sound like a possible solution at first glance and maybe one day it may become the technology of choice but its currently very expensive and does not generate nowhere near enough power at this time on a practical basis to do what your looking for.<br /><br />Bottom line is, we tend to stick with what works and despite the limitations of chemical propulsion and re-entry techniques. They do work and work well. Ultimately its going to take a combination of some event and/or the promise of great profits to move beyond current capabilities.<br /><br />Humanities progress is generally incremental, punctuated by quantum leaps at times. One day we probably will get to where your looking to go. <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>

 

[mrmorris]

<font color="orange">"OwenAnder: ...could you technically leave Earth at 1 mph as long as you never stopped gaining altitude?"</font><br /><br />You've given a velocity, but no acceleration or direction. From the way your question is stated, presumably your 1MPH is 'straight up' as measured from the launch site. Given that the velocity is negligible for the purposes of orbital calculations, I'll assume so. <br /><br />This style of question is part of the 'orbit means altitude' school of misthought. Rockets intended to place something in orbit are not designed to launch spacecraft by making them go *high*, but to make them go *fast* (i.e. 'orbit means <b>velocity</b>'). The exception is sounding rockets which are intended to go up... then come right back down.<br /><br />If it were possible to 'launch' something to orbital altitudes in the fashion you describe (100km to ~32000km), once it was *at* the intended altitude, if the mysterious force providing constant velocity were to cease -- the craft would simply fall back to earth from gravitational acceleration. It would not have the orbital velocity to counteract the pull of the Earth.<br /><br />If we assume the force holding it up never goes away, but simply stops the 1MPH velocity and 'holds it' indefinitely at the desired altitude, then there's a second problem. Everything *else* at the given altitude will be moving at the proper orbital velocity -- several kilometers per second. By contrast, the 'spacecraft' will be moving with the same velocity/rotation it had at the surface of the earth. This will vary depending on how close to the equator you were at launch, but will be something less than 900MPH. By the time you get to orbital altitudes, 900MPH will not be fast enough to circle the earth in 24-hours, and so the Earth will spin beneath the craft (the higher the altitude, the faster the retrograde progression of the craft).<br /><br />In short -- such a scheme does not have any real value in launch

 

[owenander]

There has to be SOME advantage of going straight up rather than circling Earth and reaching orbit?

 

[MeteorWayne]

If you go straight up, you come straight back down unless you escape earth's gravitational sphere.<br /><br />At least in an orbit, you stay up there.<br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p><blockquote><font class="small">In reply to:</font><hr /><p>Correct. However, by the time you reached the Moon, you would be going fast relative to other objects. You would inheirit all the Earth's speed that it has going around the sun.<p><hr /></p></p></blockquote>The moon has that same velocity, as it's in a co-orbit around the sun with Earth. Mind you -- the craft wouldn't have the correct velocity to match with the Moon's orbit around the Earth. You could certainly place the craft in the path of the moon -- and watch it go splat when the moon arrives at the same location.<p><hr /></p></p></blockquote><br />I never talked about attempting to rendevous with the Moon. Rather, I simply used its orbit as a yardstick.<br /> <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>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>We must develop new technologies. That takes research is bacsic physics and materials ...which is also being done.<p><hr /></p></p></blockquote><br />Next, we will read in Popular Mechanics or Popular Science that the "captured UFO" at Area 51 was actually a Borg sphere. Whoops, too late. The people there were just assimulated.<br /><br />Serious, the UFO conspirists would have everyone believe that Area 51 is full of advanced technology (even captured from aliens) that the government wants no one to know about. <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>

 

[Boris_Badenov]

OwenAnder asks;<br />can reverse thrusters remove atmospheric entry heating?<br /><br /> The answer is yes, if you have enough fuel or power to slow down enough.<br />By power, I mean thrust. One sure method to increase thrust & ISP is to change from a chemical reaction to a <br />thermal reaction. NASA designed, built & tested several types of Nuclear Thermal Propulsion engines starting in <br />the 1950's & continuing to the early 1970's. <br /> Using NTP Engines a ship could do things that are currently done only in Science Fiction movies. One of <br />those would be all propulsive reentry with 100% re usability of the spacecraft, including the fuel tanks.<br /> The Navy has been using nuclear engines in navel ships for almost 60 years. NASA has, is & is planning on using <br />NTG's on many space probes to supply electricity. The Russians have sent more than 30 reactors into space. <br /> With all this experience, the only thing holding us back from the unlimited potential of nuclear powered <br />spacecraft is public opinion. Until that changes we are stuck with aerobraking & relatively low powered chemical<br />reaction rockets. <div class="Discussion_UserSignature"> <font color="#993300"><span class="body"><font size="2" color="#3366ff"><div align="center">. </div><div align="center">Never roll in the mud with a pig. You'll both get dirty & the pig likes it.</div></font></span></font> </div>

 

[qso1]

The only advantage in going straight up is if you go far enough, you may be able to escape Earths gravitational influence...but at a very heavy price in propulsion mass.<br /><br />Once you have circled Earth the first time, you have reached orbit provided you sustain the proper velocity, direction, and angle and executed the required circularization burns which works to achieve the velocity, direction, and angle.<br /><br />BTW, mmorris provided a nicely detailed explanation on the 1 mph question. I assumed you meant going 1 mph on a path similar to what most current LVs use to reach orbit. <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>

 

[qso1]

Boris1961:<br />Using NTP Engines a ship could do things that are currently done only in Science Fiction movies. One of <br />those would be all propulsive reentry with 100% re usability of the spacecraft, including the fuel tanks.<br /><br />Me:<br />Unfortunately, not quite. At least not with the nuclear thermal systems tested or theorized so far. The NERVA program tested systems that had ISPs on the order of 800-1,000. This is only roughly twice the ISP of shuttle. The advantage is mainly found in sending craft on deep space missions such as humans to mars. Some of the NTP advantage is eaten up by the weight of the required radiation sheilding for crew safety.<br /><br />You are correct in the fact that you'd need enough propulsion to provide the power. Not only to slow you down but to keep you from reaccellerating due to the pull of earths gravity. The reason for this kind of propulsive power is precisely because you have to constantly work against gravity. Something currently considered the stuff of sci fi concepts such as anti gravity propulsion.<br /><br />Navy nuclear engines are substantially different in that they use heat to provide power rather than chemicals to provide reaction mass or thrust. <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>

 

[willpittenger]

Actually, I think he was talking about going straight up the whole way. <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>

 

[willpittenger]

<blockquote><font class="small">In reply to:</font><hr /><p>The Russians have sent more than 30 reactors into space.<p><hr /></p></p></blockquote><br />Unlike the reactors we orbited, most of those are making uncontrolled reentries. Ours are out there far enough that reentry will not be an issue for a long time.<br /><br /><blockquote><font class="small">In reply to:</font><hr /><p>With all this experience, the only thing holding us back from the unlimited potential of nuclear powered<br />spacecraft is public opinion.<p><hr /></p></p></blockquote><br />Hardly. Many nuclear rockets (and the atomic engines of the 1950's and 1960's) leak tremendous amounts of radiation. The joke for the early atomic bombers was that you would use only old pilots (with no reproductive plans and won't complain about radiation poisoning) and base them on isolated islands. The only plane the US flew with an operating reactor was a B-36 with with a completely unique nose with several tons of shielding. <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>

 

[qso1]

In that case, you would not achieve earth orbit at the most common altitudes. You would eventually escape earths gravity given enough propulsion. <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>