US Space Force reveals first look at secretive X-37B space plane in orbit
space.com
space.com
https://arstechnica.com/space/2024/10/the-us-militarys-x-37b...
I'm having a hard time imagining the advantage compared to being a bit closer, unless it's a more energy-efficient parking situation while the vehicle isn't in active use.
From a tactical perspective, that means this can interact with basically any other satellite.
These types of orbits also have the property that the perceived loiter time is different for the perigee and apogee.
At perigee (closest to Earth) it will be moving very fast and so any changes to velocity will have a large impact (easily change orbit).
While at apogee it will appear to sit in space and move quite slowly. As an example this is used for the Russian GPS system so their satellites can sit in high earth latitudes for longer needing fewer satellites to cover Russia.
It's used for communications satellites and is called the Molniya orbit[1]. Their GLONASS (positioning system) satellites use circular medium altitude orbits, but with a higher inclination (about 65 deg vs. GPS's 55 deg).
You may be thinking of highly-elliptical molniya/lightning orbits (1), which enabled state TV broadcasts for high-lat places in Siberia.
Burns at closest approach (perigee) have the largest influence on total orbital characteristics. Burns at furthest approach (apogee) can raise the entire orbit if desired.
(Or so I understand.)
Burns at apogee have best efficiency for out-of-plane maneuvers (change orbital inclination plane) due to lowest velocity of the spacecraft.
Highly elliptical orbits can do both at a few hours' notice.
Burns don't have to happen only at perigee/apogee so there's more flexibility in practice. And counter intuitive stuff like bi-elliptic transfers.
It's funny, I remember first learning to use such arcane maneuvers in a game called Children of a Dead Earth, in order to get into a terribly low orbit of Neptune to strike a methane refinery... My poor brain was always used to simple Hohmann transfers in games like KSP!
The US Space Shuttle could similarly "change payloads", with its modular payload bay capable of carrying either one-time cargoes (often satellites for launch), or reusable modules such as Spacelab, parts of which flew on a total of 35 Shuttle missions.
<https://en.wikipedia.org/wiki/Spacelab>
But modularity is also inherent in conventional rocket-based launches, with cargoes fitting within the fairing bay capable of being deployed or orbited.
Changing payloads in space is a rather different prospect, though the ability to rendezvous with, take on-board, and de-orbit satellites (man-made or artificial, the US's own, or other nations') is another possible capability. The X37's small size gives only limited potential here, and I'm pretty sure that if the US were snatching other nations' satellites we'd have heard about it.
https://en.wikipedia.org/wiki/Molniya_orbit
I haven't seen the orbital parameters of the X-37, so it may be in an elliptical orbit for some other reason, such as spying on or interfering with geostationary satellites or who knows what else.
A satellite in LEO already has a speed of about 8 km/s. The highest speed of a satellite in a highly elliptical orbit is 11 km/s. It you can shoot a satellite at 8 km/s, you probably can also shoot it at 11 km/s.
The problem is, of course, that the perigee of a satellite in a highly elliptical orbit can be over a different part of the planet than your SAM battery.
Assuming all else is equal (same altitude, same targeting capability, same flight characteristics), an interceptor for an 11 km/s target needs about 89% more kinetic energy than an interceptor for an 8 km/s target. Realistically, between the rocket equation and atmospheric effects, the faster interceptor would likely need to be far larger still. You're probably talking about a 2.5 to 3 times bigger missile. While a country that could develop one could likely develop the other if they so chose, it doesn't seem like a safe assumption that a country with one has the other.
If your interception point is say 500 km straight up from your launch point, just to get there you need a rocket that rapidly accelerates to over 3 km/s, and it takes a little over 5 minutes to get to the interception point. To hit an 8 km/s target, you need to fire when it is 2500 km away, to hit an 11 km/s target you need to fire when it is 3500 km away. If to score a hit you need to be within 10 meters of the target at interception, then you need to know the position and velocity of the 8 km/s target to within 4 ppm, you need to know it with an accuracy within less than 3 ppm. And note, if you are shooting from 15 km up in a fighter jet, the 8 km/s target is within your radar horizon, the 11 km/s target is not. Not to say that you couldn't build a system with target sharing and more precise tracking, but it would be a different system than the one you need for the less challenging use case.
Now it's not a strictly either or thing. You could use a missile with intermediate speed and fire it less early. There's a whole continuum of solutions, but it will always be harder to hit the faster moving target. And of course you have real world things to consider like if the target has any maneuverability or countermeasures and how much variation in conditions you can afford. Generally you are already using the best targeting system you can get and are already in the most advantageous position you can be in, so the knob you can turn is "how big of a missile do I need to get the performance I require?"
Dealing with evasion is a whole other matter. A stationary iceberg can hit a ship that tries to evade if it does so too late. Conversely simple error in your knowledge of a ship's position and velocity can cause it to be miles away from where you expect it later in the journey.
The parent is incorrect. You know approximately where it is. If your approximation is off by some amount, you miss. How good of an approximation you have is determined by your detection equipment. How good of an approximation you need is determined by the speed. For the same detection equipment, hitting the faster moving thing is harder.
> I'm struggling to understand the case where you are further from the destination than the x37B, with an orbit 60,000km from earth.
Well yeah, that's because the x37B interception scenario is the second case, where you are much closer to the destination but going much slower.
Again to clarify, no one here is arguing that to intercept a target you have to be moving faster than the target. The argument is you have to be moving faster than the minimum speed required to hit a slower target.
In math terms, you have two targets with velocites V1 and V2. To intercept there is some minimum velocity for each, v1 and v2. This is the best case scenario, you are perfectly in position, you can launch at the earliest possible time. v1 < V1 and v2 < V2 are both true. But since V1 < V2, v1 < v2 is also true. An interceptor that can achieve v1 doesn't necessarily have the capability to achieve v2.
Lower orbit = faster velocity.
So your screaming by over Emutopia's enrichment plant, and trying to take photos.
Telephotography might be an easier solve than faster image capture for the same resolution and clarity. A higher orbit means you have to do less drastic tracking corrections to observe the same area while over it.
Alternative: it's a space plane and has been mentioned it uses aero braking for orbital adjustments. A highly elliptical orbit imparts a significant chunk of potential energy that can be expended for orbital changes using aero braking instead of needing to expend limited propellent.
Source: personal experience with several hundred hours of KSP.
more range the merrier in case there is alien invasion. you would need aircraft that allow travel interplanetary system
When you are in a highly eccentric orbit (meaning the point in the orbit farthest from Earth (apogee) is much higher than the lowest point (perigee)) like this one there are several maneuvers you can do to significantly change your orbit with relatively little energy. The article describes some of the things they are testing.
A small breaking burn at apogee will lower the perigee into the upper atmosphere and they can then do aerobreaking (use atmospheric drag to lose energy) to slow down enough to land.
As an aside, it's sad about KSP2. We need a good, open-source space simulator in the spirit of KSP, which has incredible enthusiasm in the modding community.
By carefully timing boosting burns at different points in the orbit, you can change the orbit to become highly inclined - go prograde at the periapsis, and your raise the apogee.
From the image, I guess they are in a Molniar orbit [1].
https://space.skyrocket.de/doc_sdat/x-37.htm
This source indicates an 38,000 km apogee, which is is about 1/10 the distance to the moon, and just barely beyond geostationary.
Marketing of secret projects is a tricky business!