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You are most likely seeing an artifact of how JPL represents its ephemerides for fast numerical computation. JPL integrates the equations of motion over time. This inevitably results in mismatches between the integrated state and observations. These errors are used to adjust initial states and the integration is then re-performed. The cycle stops when the ...


14

Halo orbit families exist near the L1, L2, and L3 librations points. This video focuses on the L1 and L2 halo families. There are northern and southern families at each of the libration points. The northern family is identical to the southern family but mirrored across the x-y plane. At each point, the family bifurcates from the planar Lyapunov family of ...


13

Halo orbits and their cousins Lissajous orbits (like the one DSCOVR is in) around the Sun-Earth L1 and L2 have periods of about a half-year. They are not generally stable and they want to "unwind" along what's called an unstable manifold. In this question I link to Roberts 2002, The SOHO Mission L1 Halo Orbit Recovery From the Attitude Control Anomalies of ...


9

There are several reasons why spacecraft are sent into pseudo-orbits (they aren't actually "orbits") about the unstable Lagrange points. The least important reason is that only one spacecraft can be at one of those Lagrange points. Wide pseudo-orbits allow multiple spacecraft to simultaneously operate in the vicinity of one of those Lagrange points. More ...


7

eRosita is on its way to an elliptical orbit around L2 (with L2 in the centre of the ellipse). (image source: https://www.slideshare.net/esaops/wilms, p. 19) According to Merloni et al. (2012, https://arxiv.org/abs/1209.3114), the semi-major axis is planed with about 1,000,000 km and the orbital period should be about 6 months. Taking a look into the ...


7

I don't have too much time to research as I'm about to head off to work, but a quick investigation of the JWST doesn't show anything that could be used for Astrogation. Curiosity can do its own pathfinding in part because of the programming genius of its creators, and also because of how easily detectable the obstacles are. A camera can easily detect a ...


6

As the halo orbits grow out of plane, their orbital periods generally decrease. You can see a plot of the period (in days) of the L1 and L2 halo families at the Moon as a function of the closest approach distance from the Moon (rp) in Figure 2 of this paper: https://engineering.purdue.edu/people/kathleen.howell.1/Publications/Conferences/2017_AAS_DavPhiHow....


5

In fact, they are the preferred option among other staging orbits by analizing multiple factors: EARTH ACCESS: A study considering NASA SLS and Orion performances was carried out. Since SLS places Orion in a trans-lunar trajectory, Orion vehicle has to carried out orbital maneuvers to reach a orbit near the Moon, so the limiting factor will Orion's ...


5

Basically, it would not be orbiting L2 in a Keplerian orbit sense. There is no mass at L2 for the spacecraft to orbit, you are correct in that sense. The JWST would be in a solar orbit in that would normally be a little longer than one year and would use the contours of the gravitational fields from the Earth and the Sun around the Earth-Sun L2 point to ...


4

Halo orbits are a sub-class of Lissajous orbits. So that image showing a simple circular-ish orbit is just showing a 1:1 Lissajous pattern. These Lagrange-point orbits are really orbiting around the larger body, in a way that's resonant with the smaller body. If we talk about the Earth-Sun system, then satellites like DSCOVR, SOHO (L1) and the (hopefully) ...


3

tl;dr: For a given pair of bodies in circular orbits around their center of mass, there are two symmetric families ("Northern" and "Southern") of proper halo orbits associated with each of the Lagrangian points L1, L2, and L3. We usually only talk about those with L1 and L2 because L3 is so far away from the secondary body (Earth in the case of Sun-Earth ...


3

The Earth-Moon L2 is located about 1.16 times as far from the Earth as the centre of the Moon (wikipedia, so the Earth is about 7 times as from L2 as the Moon is. Since the Earth is less than 7 times the Moon's diameter the Moon would protect a telescope at L2 (or in any small halo orbit around it) from all radio noise directly from the Earth and from LEO. ...


3

One thought is traffic collisions. Once you put the first satellite exactly at the L point in question no other satellites can occupy that position. And because that are gravitationally stable points shifting them out again at the end of their life time is relatively expensive. So to be good neighbors to the other missions in the neighborhood you will prefer ...


3

If you haven't looked there before, the starting place for all NASA data is the NASA Space Science Data Coordinated Archive (NSSDC). Back in the day when I used to work with ISEE-3/ICE data, they were the place were you went to get your data or you sent it to archive your data. I'm not familiar with the data format you are asking about, but the orbital ...


3

The State Transition Matrix (STM) The STM is a linearization procedure of a dynamical system. It can be used for any non-linear dynamical system and is used to approximate the dynamics of a system over short period of times. In astrodynamics, it is used especially for statistical orbit determination (stat OD) and the circular restricted third body problem (...


3

I'll try answering your two questions simply first. If these responses are too simple or miss the mark, let me know, and I'll edit the response. 1) What are the state propagation vector and State Transition Matrix (STM)? The state propagation vector is simply the position & velocity at a given time. The STM is a matrix that captures the sensitivity ...


3

We want to find NEOs that are inside Earth's orbit, like Atens, and telescopes don't like looking close to the Sun. So the more inside the orbit of the Earth you can get, the more new NEOs you will find without having to look at the Sun. Ideally you'd like a NEOCAM near the orbit of Venus. Then you'd be able to catch 'em all. But at E-S L1, you'll find most ...


2

Short answer is no--JWST does not manage its orbit corrections itself. Stationkeeping is done from the ground. During normal ops ,there are both medium-gain and high-gain antennas on the sun side, which can be used to receive commands and transmit telemetry and ranging/doppler information. This ranging and doppler is sufficient to manage orbit corrections ...


2

This is a supplementary answer because it still involves geometry, even though it's really future geometry. tl;dr: Large halo orbits are definitely preferred to small halo orbits because the small ones are not halo orbits! They will be criss-crossy Lissajous orbits and sooner or later end up along the axis between the two bodies (geometry reasons) even ...


2

Additional useful property of large orbit is easier avoidance of eclipses: Gaia paper "GAIA: TRAJECTORY DESIGN WITH TIGHTENING CONSTRAINTS" 2014: Due to the size of the Lissajous orbit to be limited to less than 15◦ unfavourable conditions with respect to the moon can occur, where the moon is causing a partial eclipse for a prolonged period of time (...


2

In fact it could be arbitrarily low. But wait before you rejoice. The Moon has an elliptic trajectory. This elliptic motion perturbs any orbit of a satellite in LEO. If you first assume your satellite is in the same plane as the Moon and describe the system as a time dependent Hamiltonian system with two degrees of freedom, a process called Arnold diffusion ...


2

Halo orbits definitely exist around any of the collinear Lagrange point and in most regards your comment: you see one co-linear libration point, you seen 'em all. That's what I always say is correct. Halo orbits are just special cases of Lissajous orbits. You can generate these orbits in the same way you would a halo orbit around L1 or L2 (usually some ...


2

Normally I don't answer my own questions, and certainly not right-away, but since there are forces trying to close the question in part because the answer will not be about space exploration, I'd like to get at least one answer in, and at the same time demonstrate that they are wrong. Will Kerbal Space Program 2 have Lagrange points, halo orbits, and ...


1

note: The following two questions are related, may possibly have some helpful information, but both remain unanswered: Did DSCOVR travel “along the stable manifold of it's future SE L1 Halo orbit” to get there? Can Lissajous orbits have stable/unstable manifolds? If a spacecraft was in an EM-L2 halo/lissajous orbit, and another craft would was going to ...


1

I just noticed that this scenario is also summarized in Horizons output as well: Therefore, the initial state at resumption of operations 1998-Sep-25 was integrated back to August 19 assuming a purely ballistic trajectory. Trajectory errors during this interval may be significant due to unmodelled dynamics. Stitching solutions with unmodelled dynamics is ...


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