In space, the speed at which an object can travel depends on various factors, including the propulsion technology used, energy requirements, and the effects of relativity. The maximum achievable speed for an object in space, in theory, is the speed of light, denoted as "c," which is approximately 299,792 kilometers per second or about 186,282 miles per second.
Reaching the speed of light is currently beyond the realm of our technological capabilities. As per our current understanding of physics, objects with mass require an infinite amount of energy to accelerate to the speed of light, making it practically unattainable. Furthermore, as an object approaches the speed of light, relativistic effects become significant, making it increasingly difficult to reach or exceed that velocity.
In terms of current space exploration and travel, our fastest spacecraft have achieved speeds of about 17 kilometers per second (km/s) or approximately 38,000 miles per hour. For instance, NASA's Juno spacecraft, launched in 2011, reached a speed of about 70,500 kilometers per hour (43,800 miles per hour) during its mission to study Jupiter.
Efforts are being made to develop advanced propulsion systems, such as ion propulsion and nuclear propulsion, that could potentially increase spacecraft speeds in the future. However, even with these advancements, it is unlikely that we will reach anywhere near the speed of light in the foreseeable future.