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>> Eventually, Rocket Lab says it will be lofting payloads up to 150kg (331lbs) into a 500km-high orbits that go from pole to pole. My first reaction was surpr

>> Eventually, Rocket Lab says it will be lofting payloads up to 150kg (331lbs) into a 500km-high orbits that go from pole to pole. My first reaction was surprise at the launch-site, since I know much trouble has been taken to be near the equator for launches to aid in achieving orbit (for many types of orbit). Does it help to be closer to the pole for polar orbits? I wouldn't have thought it would make a difference, but this is the first time I can remember I've read about a launch so far from the equator. edit: Wow - my mental image of where Orlando and Kazakhstan were relative to the equator is WAY off. Orlando sits at about 29* N, and Kazakhstan is about 40* N at best - further than the site in New Zealand. I guess that's just about as far south as the US and Soviet Union could practically get, respectively. Although I'm still curious about the optimal launch site for polar orbits.

karkisuni 9y ago
Helps to be near the equator for two reasons: 1) the earth's rotation is added to your speed, so it takes less energy to get to orbital velocity. Further away from the equator, the less you're moving in the same direction as earth. 2) geosynchronous orbit is a very popular destination and requires the satellite to be at a very specific height directly over the equator. Starting at the equator makes this a whole lot easier. Neither of those apply to polar orbits. Going south is just as easy no matter where you are.
emiliobumachar 9y ago
In fact, I've heard that for polar orbits, you actually have to spent extra energy to cancel out all that speed you got for free - in the wrong axis - from Earth's rotation.
- chimere 9y ago
  That's right. The most common polar orbits, sun synchronous orbits (SSO), are actually inclined at ~97 deg from the equator. This means that they're moving slightly opposite of the earth's rotation, requiring it to be more than cancelled out. This means that polar launches benefit a bit from launching closer to the poles where the Earth's surface velocity is lower. However, in reality the difficult logistics of building an arctic launch site mean that this is rarely done.
  - emiliobumachar 9y ago
    "rarely done"? Has it ever been done?? Searching for "polar launch" found nothing. (There's actually a Polar Satellite Launch Vehicle [1], but it does not launch from the poles [see Launch History at 1]) [1] https://en.wikipedia.org/wiki/Polar_Satellite_Launch_Vehicle https://en.wikipedia.org/wiki/Polar_Satellite_Launch_Vehicle
jccooper 9y ago
Location essentially doesn't matter for polar orbits, other than for safety purposes. (Technically, most polar orbits are not quite 90 degrees, and thus get some benefit from the Earth's rotation, which is greater when closer to the equator. But for high-inclination orbits, the cosine losses mean that this is a pretty marginal effect.) Electron will be mostly used for low-orbit missions, as geosynchronous sats will generally be too large for it. GEO missions are equatorial, and will benefit from being launched close to the equator. Small sats in low orbits will generally be observation (which often go into a sun-synchronous orbit, which is nearly polar) or radio relay constellations (which will go into highly-inclined orbits like 60 degrees). So for the likely payloads, their launch site is just fine. And, in reality, the benefit of equatorial launch isn't generally big enough to overcome logistical problems. Only Arianespace has bothered to establish a remote equatorial launch site... because Europe has essentially no appropriate launch site and they had to put one elsewhere anyway.

karkisuni 9y ago

Helps to be near the equator for two reasons: 1) the earth's rotation is added to your speed, so it takes less energy to get to orbital velocity. Further away from the equator, the less you're moving in the same direction as earth. 2) geosynchronous orbit is a very popular destination and requires the satellite to be at a very specific height directly over the equator. Starting at the equator makes this a whole lot easier. Neither of those apply to polar orbits. Going south is just as easy no matter where you are.

emiliobumachar 9y ago

In fact, I've heard that for polar orbits, you actually have to spent extra energy to cancel out all that speed you got for free - in the wrong axis - from Earth's rotation.

chimere 9y ago
That's right. The most common polar orbits, sun synchronous orbits (SSO), are actually inclined at ~97 deg from the equator. This means that they're moving slightly opposite of the earth's rotation, requiring it to be more than cancelled out. This means that polar launches benefit a bit from launching closer to the poles where the Earth's surface velocity is lower. However, in reality the difficult logistics of building an arctic launch site mean that this is rarely done.
- emiliobumachar 9y ago
  "rarely done"? Has it ever been done?? Searching for "polar launch" found nothing. (There's actually a Polar Satellite Launch Vehicle [1], but it does not launch from the poles [see Launch History at 1]) [1] https://en.wikipedia.org/wiki/Polar_Satellite_Launch_Vehicle https://en.wikipedia.org/wiki/Polar_Satellite_Launch_Vehicle

jccooper 9y ago

Location essentially doesn't matter for polar orbits, other than for safety purposes. (Technically, most polar orbits are not quite 90 degrees, and thus get some benefit from the Earth's rotation, which is greater when closer to the equator. But for high-inclination orbits, the cosine losses mean that this is a pretty marginal effect.) Electron will be mostly used for low-orbit missions, as geosynchronous sats will generally be too large for it. GEO missions are equatorial, and will benefit from being launched close to the equator. Small sats in low orbits will generally be observation (which often go into a sun-synchronous orbit, which is nearly polar) or radio relay constellations (which will go into highly-inclined orbits like 60 degrees). So for the likely payloads, their launch site is just fine. And, in reality, the benefit of equatorial launch isn't generally big enough to overcome logistical problems. Only Arianespace has bothered to establish a remote equatorial launch site... because Europe has essentially no appropriate launch site and they had to put one elsewhere anyway.