- It was very tempting to run this doc through a LLM to make sure we don't have too many offset phrasings and typos. But I want to keep this devlog as authentic as I can, which means there will be no use of AI - so do bear with me and my - at times - quirky sentences.
DeltaV
This is an important concept. One that will become (is) the baseline for all space travel. No matter what you do, dV is key.
DeltaV: Change in velocity.
This is important because this is what tells us how much fuel and power is needed to achieve a certain goal.
For example, the math behind a mission - if done right - can significantly reduce the dV required thus increasing a mission lifetime as the mission can be completed with more fuel remaining.
In this example, we don’t care how we got into space (but this is equally important), we care about how we can achieve our goal when we are IN space. And this is where dV is important.
Travelling towards a target, moon, planet, …, we need to know how big of a change we have to do in our speed. By knowing this, we know what we need to carry to make it happen.
In a world with no limits, we could “carry” enough dV to simply fly in a straight line from A to B. But where's the fun in that…
Everything moves, nothing is stationary, timing is key.
A trip to Venus
It's tempting to draw a straight line going there - and also impossible considering the cost that would be involved.
So to get this right, we need to calculate a trajectory. And since Venus is orbiting the sun faster than Earth does (as it's closer), we need to find the right time to do so.
And it's not when Venus is closest to the earth (remember, everything is moving - quite fast).
Reaching Venus is a problem of orbital geometry. We can solve a min dV transfer (Hohmann or Lambert), launch at the correct phase angle, and only then check if our dV budget can support this trajectory
- Cheapest launch window, to intercept Venus from Earth. Note that this means waiting around 3 months to catch the window (and an additional 7 months for flight)
Below is a trajectory example of our trip to Venus. This Hohmann solution uses the best launch window, thus getting us the lowest possible dV.
The launch window is in 3 months, and flight time to Venus is 7 months.
- Cheapest dV flight from Earth to Venus.
If we were to take a trip to Saturn instead, which is a lot further away, the story is different.
Below is an example of the lowest possible dV flight from Earth to Saturn. We will depart in 2.5 years, and our flight time will be 2 years and 7 months.
Since planet alignment is key to get the best trajectory, we need to wait until Saturn is positioned best (Potentially waiting many years, but in this particular case, max time till launch was set to 1000 days)
Also notice how the ship appears to lose speed as it advances further from the Earth. It's really not, but this is the consequence of the Logarithmic scaling I mentioned in my previous post.
- Lowest dV flight to Saturn. Departure in 2 years 6 months. Flight time 2 years 7 months.
So to get all that working so we can actually plan a spaceflight, we need a flight computer that can do the calculations for us and give us the best results.
Below is an example that gives us a few options. The lowest dV solution needs around 5,000 m/s.
- Trajectory solutions for Earth-Mars. Green is lowest dV at around 5,000m/s
It's all about energy, cost and patience.