Centaur upper stage question

[rybanis]

Question: What is the preformance difference between the 1 engine and 2 engine versions? I know they use 2-engine for geostationary orbits, and they use 1-engine for outbound stuff...so what gives? <div class="Discussion_UserSignature"> </div>

 

[edkyle98]

"Question: What is the preformance difference between the 1 engine and 2 engine versions? I know they use 2-engine for geostationary orbits, and they use 1-engine for outbound stuff...so what gives?"<br /><br /><br />Atlas V (and Atlas III before it) can get away with single-engine Centaur because the Atlas booster stage is powerful enough to do most of the heavy vertical lifting against gravity, leaving the Centaur stage the job of horizontal acceleration, which can be done with lower thrust-to-weight ratios. With light GTO or earth escape payloads, the Atlas boosts Centaur toward a "lofted" trajectory apogee from which the upper stage actually descends a bit during its burn.<br /><br />An Atlas V would typically only use the 2-engine Centaur for low earth orbit missions which can involve much heavier payloads. For example, an Atlas V-402 can boost 12.5 tonnes to LEO while an Atlas V-401 would be used to lift a bit less than 5 tonnes to GTO. A fully loaded Centaur weighs about 23 tonnes. An RL10A-4-2 provides about 10.1 tonnes of thrust. To date, all of the Atlas V missions have used 1-engine Centaurs for either GTO or earth escape missions. <br /><br />The most recent dual-engine Centaur flew in 2004 on the last Atlas IIAS. The smaller Atlas had a less-powerful booster stage than Atlas III or V, so it needed the 2-engine Centaur. <br /><br /> - Ed Kyle

 

[propforce]

As a general rule of thumb, any GTO missions need only use a 1 engine Centaur, where as LEO orbit is where a more powerful thrust on the upper stage is needed hence the 2 engine Centaur. <div class="Discussion_UserSignature"> </div>

 

[willpittenger]

What does GTO mean? <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>

 

[drwayne]

Geostationary Transfer Orbit<br /><br />Wayne <div class="Discussion_UserSignature"> <p>"1) Give no quarter; 2) Take no prisoners; 3) Sink everything."  Admiral Jackie Fisher</p> </div>

 

[edkyle98]

Geosynchronous transfer orbit. Geostationary communication satellites work in 24 hour orbits above the equator that are at about 35,000 km altitude. Typically, a launch vehicle for this type of satellite is contracted to place the payload into a transfer orbit with an apogee of about 35,000 km and a perigee that can be 200 km or lower, but can sometimes reach several thousand km. This egg-shaped transfer orbit is called a geosynchronous transfer orbit (GTO). The satellite usually carries a propulsion system to provide the final apogee kick burn to circularize the orbit at 35,000 km and to reduce inclination. The orbit is geosynchronous if it is a 24 hour orbit. It doesn't become geostationary until it is a 24 hour orbit with 0 degree inclination so that the spacecraft appears to hang motionless above one location. It usually takes a few weeks to trim the satellite into a true geostationary orbit. <br /><br />Sometimes the launch vehicle performs the apogee burn. On several Titan IV missions, the Centaur upper stage performed three burns. The first placed the stage/spacecraft stack into a low earth "parking" orbit. The second put the stack into GTO. The third was an apogee burn (perfomed at first apogee) that placed the vehicle into geosynhronous earth orbit. The EELV Heavy launchers can fly similar profiles.<br /><br /> - Ed Kyle

 

[willpittenger]

Would the sat launched via a Centaur GTO burn use its own thrusters to enter the final orbit? <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>

 

[propforce]

<font color="yellow">Would the sat launched via a Centaur GTO burn use its own thrusters to enter the final orbit? </font><br /><br />If the mission is specified as a GTO mission, then it is implied that the Upper Stage will "guarantee" you to the Geo Transfer Orbit and send you on your way. Once the satellite reaches the Geosynchronous Orbit (GEO), it's upto the satellite to use its own propellant to kick in and "circularize" (so to stay on) the orbit. <br /><br />Both Centaur and Delta IV (and I assume the Ariane does the same) offer a "3-burn" GEO mission so the Upper Stage goes along with the satellite to GEO and perform a 3rd burn to circularize the orbit. This way, satellite manufacturer saves the extra weight and volume for the satellite station-keeping propellant system so it can have a longer on-orbit life. Once circularized, the stage separates from the satellite and performs a "de-orbit" manuever. <div class="Discussion_UserSignature"> </div>

 

[willpittenger]

Then, counting the deorbit manuever, that is 4 burns. <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>

 

[propforce]

<font color="yellow">Then, counting the deorbit manuever, that is 4 burns. </font><br /><br />No. De-orbit manuevers do not need to use the "main engine" but instead uses much smaller attitude control thrusters. The difference is 20K lbf vs. 10~15 lbf of thrust. <br /><br />Here's a Wikipedia link explain more about how to do orbit transfer, called Hohmann Transfer with illustrations. <div class="Discussion_UserSignature"> </div>

 

[willpittenger]

I know how the orbit works. I just was not sure what was doing what burn and with which engine. <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>

 

[3488]

Hi all,<br /><br />I thought that redundant Geostationary satellites were shunted outwards into a higher 'graveyard' orbit, to free up slots in the geostationary orbit for newer satellites, rather than 'deorbited' like LEO satellites?<br /><br />I understand that the intention is there to 'deorbit' the Hubble Space Telescope using an unmanned solid stage.<br /><br />Also is it true that it is easier to put hardware into a Heliocentric orbit like the Spitzer Space Telescope than into a geocentric orbit like Hubble or the ISS?<br /><br />If so, the Soviet Union pulled off something really remarkable with Sputnik.<br /><br />Andrew Brown. <br /><br /> <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[willpittenger]

Geostationary satellites are moved into orbits farther out. It would appear, however, their booster stage is another matter.<br /><br />I do not know what the Hubble-deorbit plans are. However, the plan to robotically service it has been scrapped. That would have attached some sort of engine. Most here are hoping Hubble can be serviced by and orbiter one more time. That mission could attach a deorbit engine. <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>

 

[3488]

Cheers wittpitenger.<br /><br />I did not realise the Hubble deorbit plan had been dumped. Hubble MUST be serviced at least one more time, now that we have had a successful Atlantis launch, not too long after Discovery, IMO raises the possibility of a Hubble Mission in the not too distant future.<br /><br />Andrew Brown. <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>

 

[willpittenger]

I would rather the engine you mentioned put Hubble into a really high orbit were it could wait for an orbiter that would succeed STS and Orion to pick it up. This orbit would be higher though than where Hubble has been released in the past. Much higher. It would probably have to be out near parking orbit. <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>

 

[MeteorWayne]

willp, I really like that idea.<br />Who knows what we might be able to do with it in a quarter of a century or so.<br />If a safe parking orbit could be found, use an ion engine and slowly boost it there.<br />It seems such a waste to just burn it up.<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]

Its orbital tilt would presumably keep it away from GEO slots. A highly elliptical orbit might help avoid collisions, but speed up orbital decay.<br /><br />Actually, though, we should move this to a new thread to continue the discussion. <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>