ISRO reached Mars on a weak rocket by looping Earth seven times

Reaching Mars requires accelerating a spacecraft to escape velocity and onto a precise interplanetary trajectory, work usually done by a single powerful upper-stage burn from a heavy-lift rocket — the kind NASA had and India, in the early 2010s, did not. ISRO's workhorse launcher, the Polar Satellite Launch Vehicle (PSLV), was built and proven for lower-energy jobs: putting satellites into Earth orbit, not flinging a probe across interplanetary space in one shot.

The default approach to an underpowered launcher is simply a bigger launcher — more thrust, more stages, more propellant, which is the capital-intensive path every established space agency has generally taken. ISRO's engineers instead treated the PSLV's insufficient single-burn thrust as fixed, and asked whether the required total energy could be delivered in installments instead of in one go, trading time for the rocket power India didn't have.

Looped Earth seven times, firing briefly at perigee each pass to accumulate velocity incrementally, matching one big burn's effect with a weak rocket.

Orbital mechanics allows energy to be added incrementally without loss, so repeated burns at perigee accumulate velocity as effectively as one large burn.

The PSLV's insufficient thrust was fixed, but the mission had schedule slack, so trading time for rocket power was affordable.

Each small burn raised the orbit's apogee, progressively increasing energy until escape velocity was reached on the seventh burn.

This avoided the capital-intensive path of building or buying a heavier rocket, keeping the mission cost at a tenth of comparable NASA missions.

When you lack the power for one decisive push, see if the same total effect can be built from smaller increments using a resource you have plenty of—here, time and orbital passes.

The mission cost about $74M, a tenth of NASA's contemporaneous MAVEN mission, and reached Mars orbit on its first attempt. Mangalyaan made India the fourth space agency ever to reach Mars and the first to do so on a maiden attempt, establishing ISRO's low-cost mission-design approach as a template it repeated on later missions and that other emerging space programs have since studied as proof that orbital mechanics can substitute for rocket power.