# Tag Info

9

Why does it look like SpektrRG makes a u-turn in the ground track image? An L2 injection trajectory looks a lot like going straight away from Earth -- i.e. the ground-track position in inertial space is changing only slowly. Meanwhile, the Earth is rotating Eastward underneath that point, so the ground track appears to move Westward across the surface of ...

7

Yes this is absolutely a thing. Delta-V can indeed be traded off in a continuous fashion for total flight time (i.e. uses more dV, but lowers transfer times, relative to a Hohmann transfer). Furthermore it's pretty directly analogous to a Hohmann transfer. I don't know a name for this but the heavily simplified version of this 'partial Hohmann' transfer is ...

7

When calculating the future orbit of an artificial (Earth) satellite, is the moon's gravity significant or insignificant? It's a great question! Of course everyone's definition of "significant" will be different. Gravity is a long range force, it never goes to zero, and decreases only as $1/r^2$. Nothing blocks it either, so basically everything pulls on ...

7

Is it... the gravitational potential energy of one pound hoisted one foot in a constant gravitational field...? Yes indeed it is! To be energy, the pound has to be parallel to the foot. $$E = \int \mathbf{F} \cdot d \mathbf{s}$$ To be torque, the pound has to be perpendicular to the foot $$\tau = \mathbf{r} \times \mathbf{F}$$ 1 foot-pound (or pound ...

6

Welcome to the site ThaNoob! I believe the answer to the question you are asking is yes, just pay attention to your choice of coordinate system. You can eliminate the fictitious coriolis and centrifugal force terms through your choice of an inertial reference frame no matter the coordinate system. However, there may still be a "coriolis" and "centrifugal" ...

4

ANone's answer address how delta-V and trip time trade off with each other, and what to consider when designing a mission. The other part of the question: Is there any open-source or freely online tool to calculate and simulate such transfers? Yes! They are called Lambert solvers. They plot a 3-D graph of delta-V versus trip time and departure date ...

4

To reduce the time for craft to reach the station, the ISS needs to be at the correct point in its orbit (or "phase") relative to the launch site at the time of launch. Doing this requires changing the orbit, either higher or lower to increase or decrease the orbital period. While most burns are done to increase the altitude, in 2015 the decision was that ...

4

Ok since you know everything except those two parameters, you should be able to calculate either of your two position vectors into your orbit-fixed frame. What this allows you to do is solve for elements within your direction cosine matrix relating the orbit and the inertial frame (which is what I assume your two position vectors are in). How you do that is ...

4

It will be a combination of things. Like TonyK mentioned in his comments, most of the change will occur during cis-lunar transfer. This is optimal because inter-planetary trajectories can be designed to result in an optimal parking orbit around your target planetary body. One neat trick astrodynamists use is B-plane targeting (a nice AGI article here: http://...

3

Foot-pound or pound-foot are synonymous, and represent the arithmetic product of pound (force) and foot (length). The pound (force) is the weight of one pound (mass) at the Earth's surface (somewhat imprecise because Earth's gravity field varies depending on your location, and the effective weight of an object will be influenced by the centrifugal force due ...

3

I will give my current best shot at this problem, and others should feel free to strengthen the argument with additional mathematics. (Or poke holes!) You ask two questions, I will answer the first as the second has been partially answered by the update. Are there other inclination change strategies that are more efficient for some values of $\alpha$? ...

3

You definitely have the right idea and understand some of the various ways to propagate orbits: Keplerian orbits TLEs with SGP4 numerical state vector propagation But all of these turn out to be approximations. Keplerian orbits are conic sections and assume two bodies (point masses or spherically symmetric mass distributions) and nothing else. An ...

3

It's possible that additional work has been done on this topic since the Newhall paper you linked, but if so, it does not cite that paper. There is a non-peer-reviewed paper that also allows fitting acceleration data, as well, but acceleration is not used in the JPL ephemerides. There are probably pieces of software in various places for producing ...

2

According to Wikipedia foot-pound and foot-pound-force are synonymous: The foot pound-force (symbol: ft⋅lbf or ft⋅lb) is a unit of work or energy in the Engineering and Gravitational Systems in United States customary and imperial units of measure. It is the energy transferred upon applying a force of one pound-force (lbf) through a linear displacement of ...

2

welcome to SE! The argument of periapsis is a function of the eccentricity vector and the mean motion vector of an orbit, and is calculated based on the formula: $$\cos(\omega)=\frac{\boldsymbol{n} \cdot \boldsymbol{e}}{|\boldsymbol{n} ||\boldsymbol{e}|}$$ subject to if $$e_{Z}<1, \implies \omega = 360^{o}-\omega$$ where the mean motion and ...

1

You must be using a computer from the 1960s to have even the most precise IAU earth orientation computation take "5-10 seconds". That said, computing the Earth's orientation using an extremely accurate algorithm at some epoch time and then rotating the Earth by $2\pi$ radians per sidereal day ($7.29211585275553\times10^{-5}$ radians per second) about the ...

1

The direction cosine matrix relating the orbit frame and an inertial frame is as followed. Essentially it is a 3-1-3 body-two rotation sequence. I talk about the DCM a little more in detail here (Calculate Argument of periapsis of orbit given focus and two points on ellipse). You will need to know all your orbital parameters in order to calculate this DCM ...

1

(I've omitted my original approximate answer.) It takes 3.00 days, for 46 orbits with apoapsis 394.6 km and periapsis 394.5 km, calculates section 3.2 of Earth Orbits With Repeating Ground Tracks. That paper also explains why a quickly repeating ground track is desirable. If a Soyuz launch is delayed, a new launch window for a similar rendezvous occurs ...

1

The New Horizons probe, if I read the Wikipedia article correctly, did not stay in its parking orbit for a full orbit. Less than 45 minutes after launch, it was already on its solar escape trajectory. But it did spend time on an orbital path that allowed it to get to the right position for the burn to escape velocity, consistently with the other answers ...

1

There have been projects with this intention, such as OLEV, but actually, this would only allow increasing the life of a satellite from a propellant and orbit maintenance point of view. Theoretically it is possible, but one would expect other systems in the satellite to fail, particularly the battery would loose maximum charge and panels would loose ...

1

Having asked and thought about a similar question, I think the answer is simple. Don't build accelerators for humans. Build them for cargo. The total mass of cargo that a human needs to be comfortable in space is hundreds or thousands of times her/his own mass. Efficient systems should deal with cargo. Most cargo can be somewhat g-hardened without much ...

Only top voted, non community-wiki answers of a minimum length are eligible