sight is necessary to understand the cosmos

If with sight you mean "capability of elaborating electromagnetic waves in the range of the visible spectrum", the statement is simply wrong. We have just got the report that the first image of a black hole event horizon was taken thanks to observation in the radio-frequencies.

So, no, sight is not strictly necessary to understand the cosmos. It is true that the broader spectrum one can analyze the more information can harvest, but lacking a fraction of the spectrum is no showstopper.

Also on a human scale, several space missions have succeeded in exploring space without having a camera for exploration. Just think of the Sputnik: it didn't have a camera, so technically it was blind.

And even we don't need to view something to understand it. Whoever takes calculus at a university level can describe your with extreme precision the properties of a multidimensional surface without visualizing it, just by studying the function representing it. And, if you object that calculus is not exactly a standard knowledge, even visually impaired people get a good understanding of the world without seeing it.

"We need to see things in order to accomplish even the simplest task." is quickly debunked by even the briefest consideration of lives of blind scientists here on earth.

Human's lack of natural ability to see x-rays has not diminished our capacity to detect, measure, utilize, and interact with x-rays.

If a society develops to the point of being able to produce electronics and radio technology, then they will have little trouble "discovering" the stars. If they cannot 'see' something naturally, then they will be able to build tools and systems to translate emissions into a data-stream that they can interact with. Exactly the same as humans have done.

Can't see something in nature? Observe its effects as it interacts with something else that you can detect, and use that property to study the phenomenon.

Can't see x-rays? Observe how they cause some materials for fluoresce when struck with x-rays, and use that to explore, study, and refine how you can interact with them.

Can't see anything? Observe how light interacts with specific electronics, and develop a photo-diode or similar to construct tones or vibrations that you can observe, and build that into greater and more refined sensing technology.

You may wish to consider the fact that earth has blind astronomers. There is far more to space related research than being able to see it with your own eyes.

I think my answer is: Yes.

Given only echo location it is not possible to discern anything in space or to orient oneself in space. However, to develop space travel, I suppose these aliens would require a high level of technological sophistication anyway. Otherwise some bat would just fly in the direction of "up" and suffocate. Word might get around that this is a bad idea.

If they first develop machinery to enhance their abilities sufficiently they might also realize that space is not just infinite emptiness.

A possible riff off of an echolocation like solution would be to release hundreds of small disposable probes that explode on impact with anything. Then light sensors the aliens have built could read the incoming data, and map out what is around them as a data point in 3D space. They would possibly be able to visualize any object based on their ability to memorize the coordinates reported by their machine, or have the machine create a model in UV or sound that they could "see" or understand. It's kind of like how a cats whiskers provide acute and specific sensory feed back from a specific point which allows the cat to make adjustments to their location with high precision almost instinctively.

Of Course!

That is, assuming these people have the intelligence, resources, sciences, temperament, desire, technological advancements, etc., etc.

If you can see this in the sky:

And something like this orbits your planet:

Then you're more than equipped to get out and take a good look at this:

All of those things should be "visible" to a species who can see magnetic fields the way we see light.

I think your aliens would be better adapted to space exploration than humans are.

Echo location is a spatial sense. It gives you directions and distances and via Doppler shift changes in distances. A species with a sense like that would be able to understand something like the solar system much better than a species that relies on a planar sense tricked up to boost hand eye coordination so that you do not fall out of a tree.

It also maps directly into radar which works with exact same principles and has exact same limitations and advantages. Except it works in space. And radar is a human version so it needs a conversion to something us poor humans can understand. Your aliens would do much better since they would understand all the data about spatial data and movement directly.

You'd need an "echo display" that gives the proper audio response based on computer data and the sounds it receives but apart from being larger and lower resolution that visual analogues it is not that complex.

Generally changing vision to echo location loses things useless for space exploration such as ability to see detail and color and gives useful things such as better spatial sense and sense of motion.

And they also have a superior magnetic field sense. They could sense the planetary magnetic field, large ferrous objects moving in it, the direction the solar wind is coming from. They'd probably know where the sun is even at night.

In space they'd probably feel the solar magnetic field. Certainly the ship could have systems to allow them to do so. And to feel the movement of the ship and even the movements of the planets. Or other ships. And then there is the glorious stuff elemtilas talks about.

It's well within the realm of possibilities. Vision is only necessary for us to because it is what we know. If your alien race's dominant senses are as effective for them, as sight is for us, then they could, quite possibly "sense" the nature of the cosmos in their own way.

As humans, our technology has allowed us to overcome our physical limitations over and over again. If your aliens are intelligent enough to create sophisticated technology. And it evolves similar to ours, then (I would think) lack of sight should be an easy hurdle to jump.

But, when talking about space, sight is necessary to understand the cosmos.

Really? Or is it just necessary that they be spatially aware?

Open your mind. It will take more work on your part, but you can explain it.

We cannot see X-Rays, but we discovered them... and then figured out how to make machines/devices that represented them in a form that we could understand (see them on photographic plates). And then discovered how they could be useful.

Note that X-Ray radiation killed a lot of the early scientist studying it (via cancer) but that didn't stop them. We learned X-Rays, and then we learned new stuff, and now we have MRIs, use sound waves to measure blood flow, etc.

The sun is easy to "see" without "vision".

They would feel the warmth, even if they couldn't see it. (Or feel effects from it if you want it really far away)

It might take longer to "see" the stars and moon(s) than the sun... but eventually a sentient species of sufficient intelligence would figure it out. First they figure out it is there, then they (eventually) figure out how to get a better view (however you decide that is possible).