Sputnik 1 only worked for 21 days until its battery ran dry, explorer 1 ran for 111 days. It wasn't until Vanguard 1 that we started putting solar panels and recharge methods on satellites. It was successful as Vanguard 1 transmitted its signals for over six years as it orbited the Earth. I want to know why the first few spacecraft in orbit did not have a way to recharge.
Functional solar electric systems are a large part a product of space related development so there simply was not an off the shelf solution.
Building a functional rechargeable battery system requires:
- Keeping the fragile glass panels intact during launch
- Getting the panels to unfold/deploy reliably (Explorer 6)
- Keeping the panels from overheating
- Keeping the batteries from freezing
- Cutting off charge current when batteries are full
- Shutting systems down to prevent fully draining battery
- Accurately tracking current battery charge
- Not weigh more than a non rechargeable system of similar operating life
Also ideally you have a reaction control system that means the solar panels face the sun.
Many of these are trivial problems now, but at a time when relays and vacuum tubes were the known/well understood electrical parts this brings challenges, since both consume substantial amounts of current in operation (tubes due the filament needing to be hot and relays in coil current) so any attempt to use off the shelf hardware would have consumed far more power than the early solar panels could provide. Early transistors were fragile and not well understood, and still physically quite large. Explorer one flew with just 20 transistors. A basic linear regulator needs around the same number, and a current solar charge controller several times that.
Having a complex power management system also brings risks in that any problem in the system is pretty much certain to kill the mission because entire craft goes dead.
These factors mean that when faced with extreme time and weight constraints and political pressure to get something, anything into orbit both US and USSR chose to stick known and reliable non rechargeable batteries into the early payloads and simplest possible power management systems and only switched to solar when the core problems of just getting to orbit had been solved and the initial flights had provided data on the environment they would operate in.
In addition most of the early satellites re-entered after a couple of weeks, so having solar power would not have extended the useful lives much in any case.
edit: Comment from Christopher James Huff links this report which notes Explorer 6 only achieved 3 months use from rechargeable Nickel Cadmium due degradation to the batteries during charge, and the later TIROS 'solved' this by only using 3% of the capacity, allowing simple charge circuit at the cost of flying 97% more battery mass. It is 1966 and the OAO series where basic battery management is used to extend battery life into years, almost a decade after Explorer 1.