How this instrument works
Travel time answers one question: how long does a fixed route take at one steady rate? The formula is nothing more than the rate equation turned around — instead of solving v = d ⁄ t for speed, this instrument solves the same relationship for t = d ⁄ v. Hold the pace constant and the answer scales exactly with the route: double the distance and the time doubles; double the pace and the time is cut in half.
Mission planners use exactly this shortcut to rough out a translunar coast before running a full trajectory model with burns and gravity assists; a logistics analyst uses it to post an ETA for a container ship holding a fixed cruise speed; a pilot doing dead-reckoning navigation between waypoints uses it with true airspeed and no wind correction. The common mistake is reading the output as a measured arrival time rather than a planning estimate — the model assumes one number for the whole route, which is rarely how a trip is actually flown, sailed, or launched.
The model breaks down wherever the rate genuinely changes along the way — a rocket burning propellant and shedding mass accelerates as it flies, a ship slows in a head sea, a car crawls through a city center and opens up on the highway after. None of that variation appears here; feed it one representative rate and it returns one average duration, which is exactly why Apollo, whose actual speed swung from an Earth-departure burn down to near zero at the point where lunar gravity took over, covered the Moon distance faster than this constant-rate estimate suggests.
- Enter the trip's total Distance in kilometers — 384,400 km is preloaded as the Earth–Moon distance.
- Enter Cruise speed in km/h, the single steady rate you expect to hold for the whole trip.
- Read Travel time; switch its unit between day, h, and yr to match the trip's scale.
- For a sensitivity check, nudge Cruise speed up or down and watch Travel time move inversely.
Worked example — cruising to the Moon at 3,540 km/h
Set Distance to 384,400 km, the Moon's average distance from Earth, and Cruise speed to 3,540 km/h, close to Apollo's translunar cruise rate. The formula gives t = 384,400 ⁄ 3,540, which works out to 390,915.254237 seconds internally — read on the Travel time field as about 4.52 days, or 108.59 hours if the unit menu is switched to h.
Real Apollo flights covered the same 384,400 km in roughly three days, not four and a half, because the spacecraft's actual speed was never constant: it decelerated leaving Earth's gravity well and accelerated again falling toward the Moon's. This instrument returns the single average rate that would cover the distance in the given time — a deliberately simplified planning figure, not a burn-by-burn trajectory integration.
Questions
What does Travel time actually represent?
The time your route takes if you hold Cruise speed constant across the entire Distance — a planning estimate, not a measured transit duration. Real vehicles rarely hold one exact speed the whole way, so treat the number as a first-pass figure to check against a fuller model.
Why did real Apollo missions reach the Moon faster than 4.5 days?
Because their speed was never constant. Loading 384,400 km and 3,540 km/h — Apollo's approximate translunar cruise rate — into this instrument returns about 108.6 hours, just over 4.5 days. Actual missions took roughly three days because the spacecraft decelerated leaving Earth's gravity and accelerated again falling toward the Moon, a swing this single-rate model deliberately ignores.
How does travel time change if I double the cruise speed?
It's cut exactly in half, because t = d ⁄ v is inversely proportional to v for a fixed distance. Raising the 3,540 km/h lunar-cruise example to 7,080 km/h drops the 108.6-hour result to about 54.3 hours — the same 384,400 km route covered in half the time.
Can I use this for a Mars trip instead of the Moon?
Yes — swap in Mars's roughly 225-million-km opposition distance and a Hohmann-transfer cruise speed near 40,000 km/h, and the readout comes to about 234 days, near eight months, in the range real Mars missions actually take. The formula doesn't care what the trip is, only that Distance and Cruise speed are both filled in.
Does this account for acceleration and deceleration phases?
No. It assumes one steady Cruise speed for the entire Distance, so launch acceleration, mid-course burns, and any braking sit outside its scope. For a rocket or aircraft with distinct acceleration phases, this figure is a coarse average, useful for a first estimate but not a substitute for a phase-by-phase trajectory calculation.
What units does the Travel time field support?
Days, hours, or years, selectable from the field's own unit menu, while Distance stays in kilometers and Cruise speed in km/h. A short hop reads clearly in hours; an interplanetary trip is easier to read in days, and a deep-space scenario can be read directly in years.