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If sending a payload to GEO (geosynchronous orbit) or any other high orbit, you could start off launching to LEO (low Earth orbit), and then use a Hohmann transfer to raise the height of the orbit. I think this is pretty much the standard of how it's done. Hohmann transfers are the most efficient way to raise orbit, but that doesn't mean that going from ground->LEO->GEO is the most efficient compared to other options.

Do launches ever bypass LEO altogether? For GEO, couldn't you just launch straight to GEO? So at an altitude of 300 km or so, you would be flying almost vertically. Is this ever done or seriously proposed for real launches? Would it be more or less efficient?

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  • $\begingroup$ LEO is usually used to ensure that the forces of launch, atmosphere and other forces haven't been detrimental to the mission or technologies. The issue is not Delta-V saved, I think the issue is ease-of-recovery given that something went wrong during the most stressful part of the mission (launch). Recovery from GEO is far worse than LEO. Source: Another answer on this site, I forget which. $\endgroup$ – Magic Octopus Urn Jun 27 '18 at 19:29
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To attempt to answer this question a little more directly, yes, there have been launches which bypass a LEO parking orbit. According to this paper, Luna-2 launched almost directly into a lunar insertion orbit (although intervening coast segments may have been "LEO", per se).

Edit: Zarya states that Luna-1, Luna-2, and Luna-3 all launched into direct lunar transfers.

As others have mentioned, though, there are several good reasons to launch into a LEO parking orbit, and that's what the majority of super-LEO missions do.

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    $\begingroup$ If you're not using a LEO parking orbit followed by a transfer orbit you are typically using "direct insertion" to some orbit or flight. The Atlas V is "capable of direct insertion into an inter-planetary trajectory." Also the Delta IV supports "direct insertion to GEO." So yes you can and we have the technology, but as others have pointed out the good reasons for not doing it. $\endgroup$ – BeowulfNode42 Mar 3 '14 at 8:07
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    $\begingroup$ I am skeptical that Luna-1 through 3 never passed through LEO. silverbirdastronautics.com/LaunchMethodology.pdf "In fact, many launch vehicles fly only a direct-ascent trajectory, even to a high or non- circular orbit. However, an observation of these trajectories almost invariably finds the launch vehicle, at an altitude of a few hundred kilometers, accelerating almost horizontally through the local circular orbit velocity." $\endgroup$ – HopDavid Sep 19 '15 at 0:50
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The common method for entering GEO orbit is to launch in what is known as a Geosynchronous Transfer Orbit (GTO), which has an apogee at GEO altitude, and a perigee of a few hundred km. Effectively all GEO missions insert their payloads into a GTO (and not into a LEO parking orbit as the OP suggests). There is no benefit of stopping in LEO first, as the only difference is that the GTO orbit has a much higher velocity at rocket burnout (it is this extra velocity which is translated into gravitational potential energy at apogee).

The booster upper stage is separated from the payload at low-Earth altitudes and the satellites coasts to apogee where it uses on-board propulsion to circularize the GTO orbit into GEO, typically over the course of several orbits. Take a look at the Falcon 9 user's guide, page 27, for how a mission to GTO looks. The main reasons to use this concept of operations are to gain the benefits of staging the upper stage rocket mass

Launching straight to GEO is practically impossible — assuming that this would be defined as the rocket being responsible for separating a payload in GEO. The only feasible means of doing it would be to add an upper stage to the rocket that would accomplish the same function that the satellite propulsion does for GTO-to-GEO circularization. But since the sequence of events in the same this is a distinction without a difference where you've just renamed the satellite propulsion system as a part of the rocket. GEO orbits are at ~42,000 km, where as high LEO is ~1,000 km. You simply have to coast your way to GTO as it takes hours to get there (using anything remotely like currently available rocket technologies).

It is worth mentioning that technically most rockets do enter LEO for some point in time, although they typically don't stay there for very long. I believe most Falcon 9 missions to GTO are in a very low "LEO" orbit for on the order of 20 minutes between first stage burns, for instance.

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    $\begingroup$ I can't think of a recent mission that has not staged in some way in LEO. $\endgroup$ – Erik Jul 22 '13 at 18:54
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    $\begingroup$ Sure, straight to GEO is possible, please correct this - it is just insane in terms of propellant etc. $\endgroup$ – s-m-e Jul 22 '13 at 22:39
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    $\begingroup$ You could go straight to GEO but still stage -- so that wouldn't be insane. $\endgroup$ – Erik Jul 22 '13 at 23:07
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    $\begingroup$ @Erik: In terms of staging you are right. Someone should explain the concept behind certain trajectories, staging and some basic orbital mechanics. This makes a lot of sense here. Otherwise this answer ^ is a bit pointless. $\endgroup$ – s-m-e Jul 22 '13 at 23:45
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    $\begingroup$ Fun video. I used to do ascent flight design at NASA and we coded our own ascent analysis tools. You can get amazing stuff for free now. STK is the standard (agi.com/products/stk/modules/default.aspx/id/stk-free) but there are others (orsa.sourceforge.net/screenshots.html). Many export great graphics that would be of use here. $\endgroup$ – Erik Jul 23 '13 at 0:59
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The reason one doesn't normally launch to GEO is that of fuel requirements.

A hohman transfer orbit is usually the lowest energy method to achieve a particular orbit other than LEO. Boosting to LEO, then using a hohman transfer orbit saves fuel, and thus launcher mass. And, since orbital maneuvering is in upper stages, typically, reducing the upper stage mass reduces launch costs.

There have been non-LEO launches; mostly, they have been non-earth-orbit trajectories.

It's worth noting that even the moon shots have generally used an Earth Orbital staging point; this allows for system checks prior to boosting for the moon. Four of the Ranger probes failed in parking orbit prior to lunar boost.

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    $\begingroup$ Satellites heading to GEO rarely enter LEO, rather, they enter a Geosynchronous Transfer Orbit, which is a highly eliptical orbit, essentially, it's a Hohman Transfer Orbit from LEO to GEO, but the satellite never actually enters LEO orbits. $\endgroup$ – PearsonArtPhoto Jul 23 '13 at 0:33
  • $\begingroup$ @PearsonArtPhoto Technically the satellite is in LEO until the GTO insertion burn. Granted, that burn often occurs before even one full orbit period. $\endgroup$ – user29 Jul 23 '13 at 1:02
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    $\begingroup$ Usually the burn is still going on when it is in "LEO", at least, from my experience. If the engine isn't off for at least a few minutes, I wouldn't say it's in that orbit... $\endgroup$ – PearsonArtPhoto Jul 23 '13 at 1:06
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    $\begingroup$ @PearsonArtPhoto Well, assuming the GTO insertion burn is going to be centered on the descending node on the first period, there is a period of free flight, and until that burn is performed the satellite is in LEO. $\endgroup$ – user29 Jul 23 '13 at 1:11
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You can't launch straight to Geostationary Orbit (GEO) as you can't get the perigee high enough without a burn at geosynchronous altitude. The Proton has done that, though with a Low Earth Orbit (LEO) parking orbit along the way. The Ariane 5 normally launches directly into Geostationary Transfer Orbit (GTO) — 250 km perigee and (close to) synchronous apogee. It has finished all its activity by about 27 minutes after liftoff.

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  • $\begingroup$ I thought some NRO launches on Atlas V go with direct to GSO insertion ? $\endgroup$ – kert Oct 29 '16 at 20:39
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India's Chandrayaan-2 was launched into an initial Earth orbit with a perigee of 170 km and an apogee of 40,400 km. Whether you count it as LEO depends on your definition of LEO. Some would count it because the perigee intersects the altitudes for LEO. Others would not count it because of its high apogee and high eccentricity.

As described in this answer and this answer, it is slowly making its way to the moon. Its engine is not powerful enough to do a single TLI burn, so instead it is taking advantage of the Oberth effect by making a burn each time it reaches perigee, boosting to a higher apogee each time. It will eventually get to the moon.

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